Sooo.... I know this is an old question but the problem I see with all the networking protocol answers (IPv4, domain renewal, etc) is that they are all so easily reversible. In the real world, when something of adequately major consequence gets turned off, it does not stay off for very long regardless of any bureaucratic or even legal concerns. Instead of thinking about what someone didn't do, think about what they did do. Perhaps instead of failing to upgrade to IPv6 it was the upgrade itself that killed it. When you try to patch things over and over to change how they fundamentally work, you often get what is referred to as spaghetti code. Badly programmed garbage that is super easy to break by accident.

Your world's equivalent of IPv4 will soon be depreciated so the development team in charge of things decide to release an IPv6 patch. But they forget to clear thier cache before running some tests; so, everything seems to be working just fine; so, they pull the trigger and send the networking protocol patch out to the world, only... it does not work at all.

Everyone who gets the bad update therefore gets cut off from the internet making fixing the patch impossible.

Not only that, but the prosthetics have no physical data ports. They are "bluetooth only" or something of that nature meaning once you break thier internet it says broken.

If technology is of human origin, it simply can't be plausibly explained with some incident at all. Period.

If rest of the tech works, then any environmental condition specific to implants is impossible.

Monopoly is impossible as well. There's not a single thing invented in last few centuries that wasn't either independently invented by other people or reverse-engineered and reproduced. Technology as crucial as something that does "99% globally" of anything, will attract attention of pretty much every superpower's government who have necessary resources to analyze the hell out of it. It works that way today and since it became more and more common comparing to the past, I don't see how it could become worse in future.

Unrecoverable error scenario is impossible. Either your broken implants can be patched or if you invent some reason to have software hardcoded in read-only manner, factory can simply start crunching out new, working implants next day.

Remote control/server/mesh failure scenario is impossible too. Right now we generally have at least one big fuckup per year (google "bgp internet down") that affects entire regions. No matter how big amount of devices and services involved, people still figure out and fix problems in a matter of days and constantly improve software/work flow to make failures rarer and recovery faster.

So, that only leaves us with idea of non-human origin: the core part of implant technology is some advanced alien phlebotinum. This is the only way you can ever explain that it have some built-in expiration countdown that humans simply can't figure out, being aeons behind this technology. This still can conflict with you story if you have any plans of reviving implants - you'd need to bring alien maintenance info that allows to revive this core into plot somehow. In form of contact with them or finding some info cache or whatever.

Considering your comments that implants are actually working, but simply not communicating, you can also play with idea that it wasn't some unexpected accident. A malicious and powerful faction carefully mapped entire infrastructure that supports implants and launched an attack that physically destroyed all the servers, data centers and backup locations across all governments and corporations. As well as personnel. Just remember that you need to plausibly explain how they came to such power to pull this stunt - it is somewhat questionable, but at least not outright impossible. The rest of "recovery" plot might go around finding forgotten home repositories and physical media backups of project alumni and piecing them together.

A shocking new discovery about the human condition.

Scientists all over the world went to work immediately in order to find a technical solution to the sudden degradation of the implants humanity has taken for granted for so long. Cybernetics, nano-engineering, medicine, and many other fields of modern science contributed to what came to be mankind's greatest concentrated scientific endeavor.

After months of searching, an international team of xeno-biologists and radiophysicists made a remarkable and ground-breaking discovery: All of humanity was interconnected with a tight, hitherto undetected web consisting of an unknown radiation, similar to electromagnetic waves. It was likely that this inter-human network had existed since the dawn of man.

Evidence suggested that the communication between implant and human body was somehow facilitated by this network, unbeknownst to the engineers who invented the very first cybernetic implants. This discovery was celebrated as one of the most significant findings in scientific history and allowed further insight into open questions of all human sciences.

Further research led to an additional, horrifying discovery. Not only did the implants make use of the inter-human network, but they also modified it. So much so that it reached the point of near collapse, causing severe fluctuations in the web, which was identified as the cause of the worldwide implant failure.

What would happen if the inter-human network would cease to exist was anyone's guess, but it seemed likely that humanity's survival was at stake.

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This answer relates to one of your comments where you mentioned that your story is based around different tribes that fight over the decision on whether to re-implement or discard the implants.

I tried to enforce this conflict by putting the survival of the human race in the hands of those who want to re-activate the implants.

Now that scientists have learned more about the way humans and machines interact, they can work towards making everyone's implants activate again, but dabbling with the fine strands of the inter-human network may put humanity at the risk of extinction.

Temporary glitch that can't be fixed without the power of cybernetic implants

This expands on the EMP/protocol error/SSL certificate out of date/millenial bug/... Basically, the problem is something well-known and theoretically simple to fix. So why can't anyone do something about it? Simply because cybernetic implants are sufficiently complex and intricate that unaugmented humans are unable to understand/interact with their technology. The sudden disappearance of all augmentations leaves humanity unable to understand their best creation (the first implants were were risky affairs, with the successes giving rise to new experiments - a messy, possibly politically problematic, affair nobody wants to be involved in).

Different types of technology

To explain why normal tech still works, cybernetic enhancements could be the result of some specific technology, that doesn't find much use anywhere else. Maybe nanotechnology is too dangerous to use in industry scales, but acceptable inside living bodies (which basically are biological nanotech). Maybe implants are grown, while the rest of the technology in the world is made from silicon. Maybe one big company made the interface technology a trade secret, but its labs got destroyed by whatever caused the incident (or its consequences - maybe the company was blamed for the malfunction, and burnt down by an angry mob). In this case, the implant technology would be deliberately obfuscated to prevent meddeling/reverse engineering - making reprogramming (or fixing) cyberware more like healing alien biology.

Something like a millenial bug would usually be relatively simple to fix - the only issue would be applying these fixes to all affected systems. But if the only institution capable of applying this fix was attacked and had its systems destroyed (which maybe even used illegal nanotechnology, so can't be rebuilt very soon), a small glitch like that could become a permanent problem.

Hackers planted encryption ransomware worm on the update servers, and pushed the update world-wide. By the time anybody knew what had happened, every single implant had installed the firmware update, and was was prevented from communicating with the user, but the moment a 'clean' implant comes onto the network, or within range of an infected implant, the worm spreads to the clean hardware. Nobody knows who the hackers were, and nobody knows what the encryption keys were, and nobody has managed to keep an implant clean long enough to do anything.

The government got hacked.

The government forced all the manufacturers of the implants to install a backdoor, which allows them to shut down implants remotely. Just in case someone decides to augment themselves up and go on a crime spree or something.

Just like the modern day NSA, they got hacked. Left the keys to the kingdom lying around on a server somewhere, or some insider leaked them, or they accidentally published the key themselves (happened to Apple).

However it happened, as soon as it got out it only took one person to send the shutdown command to every implant on the planet.

A lot of people died. Hearts stopped, aircraft pilots suddenly couldn't control their planes, some just died of the shock of half their bodies shutting down. Of course there was also a massive shortage of replacement parts without the backdoor, and many people were suspicious of them anyway after that experience.

Computer virus gone horribly wrong

There was a group of people (terrorists/totalitarian country/mafia/something) that wanted to control the implants. After all, that would give them tremendous power over all other humans.

The implants had a tough security system in place to prevent exactly this from happening, but in the end - we're all human and we all make mistakes. The group succeeded in finding a security hole that they could exploit.

So they wrote a virus that would infect the implants and open them to remote control. They were once again wildly successful, far beyond their original plans. In 48 hours, the virus managed to infect the entire population.

But the virus had a bug. 49.7 days after the initial activation it would crash and take the whole implant with it. Safeguards would kick in and prevent any damage to the human mind, but the implant itself would be bricked.

Programmed obsolescence gone wrong.

Cybernetic implants manufacturer programmed them to stop functioning after a given period of time, but an error made all of them to stop at the same time.

Chernobyl V2 the newest, most advanced, and of course the biggest radioactive power plant in history ....made a sound it should not have .... BOOM...

This caused the entire area around the plant to get radiated, but most importantly, it made a radioactive cloud that is roaming earth.

The radiation from the cloud is not strong enough to do any (significant) damage to anything biological, but it does cause the implants to give off an electrical charge that is very painful.

Making the implants radiation proof is not really viable as you would have to coat them with lead ... lead as you might know is highly toxic, and is not something you want inside your body.

While the cloud is not everywhere at once, at some point it will roamed all parts of earth, and as a precaution everyone turned off/removed their implants.

The scientists expects the cloud to have dissipated in about 50 years, but at that point are humans willing to go back to implants ? and potentially relive the nightmare ?

Retired communications protocol

Another legacy explanation - the protocol that runs the internet got taken offline. Currently we're running on IPv4, but that has a lot of shortcomings (such as there are no more free IP addresses). IPv6 has been redesigned by lessons learned from IPv4, but adoption is super low even today. It takes a loooong time to change something so fundamental. But eventually it might happen.

And then, one day, once everyone had switched over to IPv6, the ISPs of the world decided to turn off IPv4 for good. The date was set, the event was globally coordinated, the switch was thrown.

But everyone forgot about the implants. They are a complicated piece of technology which interfaces directly with the mind, so any changes to it have to be VEEEEEERY thoroughly tested. It's super expensive and kept to a minumum. Switching that over to IPv6 was on nobody's TODO list, because, hey, it worked, so don't touch it.

You can replace IPv4/IPv6 with some other, futuristic network protocol, but the idea remains. At this point, turning it back on would be a nightmare because you'd need to work out all the routing rules and IP assignments and whatnotelse. LOTS and LOTS of negotiation between ISPs, but everyone's in a bad mood...

Why not have a group of rebels that want to bring back 'real emotions'.

In Altered Carbon (The Netflix series at least) a group of societal rebels' tl;dr goal is

If we consider the downsides of augmented happiness, people could do vile things without any emotional feedback or trauma if they get a dose of pleasure from their cybernetics for each vile task they complete.

Even if you don't want vile things to be enabled by the chips, there's no reason there couldn't be a group of societal rebels that want the world of emotions to get back to 'the good old days'.

Have them infiltrate the main control 'hub' for the cybernetics software and deploy a patch that disables the chips while shredding the backups and making the storage format read-only, or some other slightly handwavy solution to stop the chips just being reset.

I'm going to propose a different direction: the failure was intended by the original designer.

While I wouldn't presume to rewrite the history of your world, this problem does invite some interesting backstory (though you may feel this rips off I,Robot a little too much).

Cybernetics, Enhancements, Plugs. Whatever you call them, everyone is using them - but few today give thought to the man who made this technological revolution possible; Dr. Brainman. On the eve of the 97th anniversary of the first public cybernetic, let's look back at his invention, and the history of these devices.

In the year 2049, the late doctor was working in the labs of MegaCorp, Inc. (known today as BrainCorp [BSX:BRC,$1.3Q]) when he discovered the key to brain-computer interaction on a 2-way, fully conscious scale. After 3 years of work, the HoloEye was released, giving high resolution, zoomable, recordable vision to the blind, and eventually everyone.

Recognizing the potential of this new device, BrainCorp has kept the exact design their most closely guarded secret, being the target of massive corporate espionage campaigns, and [...]

In reality, BrainCorp doesn't know how the device is made - they can plug anything they like into the port to create and improve upon all manner of tools and toys - but the device which enables it all is a mystery.

They even make and sell wholesale devices to other companies, so confident they are that no one else will be able to understand the device either. (And wanting to avoid the wrathful "anti-monopoly" legislation of the world government.)

Shortly after first creating the device, Dr. Brainman foresaw that his invention would be the doom of humanity. "If you give a rat a button that dispenses food, and a button that dispenses endorphins directly into his brain, the rat will push the pleasure button over and over until he dies of starvation."

But the damage had been done - he had built a machine to manufacture the devices by the billion, and he knew that if he tried to do anything to stop it, MegaCorp would throw every mind they had to discover the secrets and rebuild it. Instead, the good doctor had to play the waiting game...

In a routine update to the machine, he introduced a kill switch to the operating system of the devices - a switch which would cause the device to stop working at some future date. The devices only lasted 20 years before needing to be replaced, so eventually every device in use would have the flaw.

He set the date for 100 years after his first discovery - long enough that anyone he worked alongside, discussed theories with, or even chatted to in the cafeteria would be long gone, and no one would be able to update the machine to remove the kill switch.

Today, only a handful of people even know of the machine's existence, and none have any idea how it works - let alone how to fix it. But at midnight tonight, everyone's going to become a lot more interested...

Of course whether Dr. Brainman's prediction that humanity would pleasure itself into oblivion may not have been accurate - from the sounds of your initial description, people have been using these devices responsibly. Really this was just a fun writing prompt, but if it helps give you some inspiration, then huzzah!

In todays world the main barrier to direct brain-machine interfaces is that the body rejects implants. Typically the body will grow a barrier/capsule around any foreign object placed into the brain (in order to isolate it). Presumably they have solved this problem in your world.

That all changed when the I386 virus came into contact with the first human.
The presence of the virus slowly makes the human nervous system more sensitive to foreign objects. The high-tech bio-compatible implant materials are no longer seen as compatible by our bodies. The body then does what it normally does and isolates the implants with a layer of tissue, rendering them useless.

Sure the implants can still collect body heat and sugar from our cerebral fluid to keep operating, but without neural connections they can't do anything.

The virus only existed in 1% of the population that was living isolated from normal society. Past generations never knew about the virus it because it has no noticeable effect on normal humans. The worst part is that the virus is contagious for a long time before it causes any symptoms. By the time it was discovered millions had been infected.

The virus is an NRA type virus and mutates rapidly. By the time anyone found out what was happening there were already hundreds of variants and it was impossible to vaccinate.

Failed to renew the domain name

It's just one of the old-fashioned things again. All the implants are cloud-connected, of course. That's how they talk to each other, and smooth the communication between their human hosts. And therefore, they all have the same hostname programmed into them. It would be a real modern Babel otherwise, if your implant could only communicate with implants from the same manufacturer.

And on the fateful day, the DNS registration lapsed. That's the sort of accident that's been happening to the biggest of companies. Microsoft forgot to renew Hotmail back in 01999, and that wasn't exactly the last company to drop the ball that way. And that was the easy case, with a domain that belonged to a single company. But these implant manufacturers had teamed up and registered the domain name together.

You know what happens when everybody is responsible? Then nobody is. Sure, each company promised to renew the name in turn, for 3 years. And after 3 years the next company would pay up. The one thing they overlooked in the arrangement (and it's easy to say this in hindsight) was how company mergers would work. Oops. And since this whole arrangement worked for decades, it's not like any of the original decision makers were still around. It's just a lowly manager cutting duplicate expenses after a merger.

So, no hostname, no cloud access, and all implants go in panic mode. They're nice enough not to kill their hosts, but they can't even get the medical dossiers of their hosts, let alone communicate with other implants. Better shut down and do no damage, then. The original programmers were that smart. They just could not foresee how utterly dependent future humans would be on these implants.

The bio-cyber implants can only interface with someone infected with the otherwise generally asymptomatic Handwaveosis, which makes the brain's neurons particularly sensitive to Macguffin fields. And early bio-cyber implants would only work for a few hours before the body rejected the foreign object - only implants coated with Handwaceae spores avoid forming scabs around them.

So when that awful disease / cruel bioweapon swept through the population and wiped out that vital link in the chain, people's bio-cyber implants stopped working.

By putting the fault in the thing that doesn't exist in real life, you don't have to explain everyone's brains changing - or a society being smart enough to develop the electronics and software not being able to maintain it when it breaks.

You could also blur out the cracks in this story: Perhaps the cause of the problems hasn't been discovered yet, or it's a government/trade secret. So your protagonist has only heard a range of contradictory rumours.

The radio spectrum is full

The implants are just the peripheral that links the biological part with the actual user device (smartphone, smartwatch... whatever they use in the future). That devices are where the processing power really is, the implant simply serves as a link with it, over low-frequency radio (think Bluetooth).

They worked very well initially, when just a few people had implants, and they hold at most 1-2 implant-linkable devices. But then, we got to a situation where everyone had an implant operating on that frequency. Moreover, due to customer demand everything you buy now is implant-capable: your TV, doors, windows, fridge, bulbs... all of them are smart-things that you can control from your implant.

Five years ago the predominance of these items got to its peak, leading to the spectrum being saturated, and implants no longer working (or, more exactly, they work errantly. If you are lucky it might work, but more often than not, it will be unable to communicate with it).

They are all working on a free range of the spectrum, similar on how your garage opener works at the same frequency as your WiFi and your microwave nowadays and, while it doesn't reach too far, it is a very limited range where they can operate, mainly due to the low power requirements. Even if you were willing to change your implant in order to use a different frequency, going to an higher power one would likely fry your brain (in fact, some of the implants that were manufactured in the later years, were using more energy than advisable in order to produce a working signal -and not just as a punctual event, but continuously-, and are quite risky to use). These people were cyberpunks, not idiots.

Theoretically, you could get them working if you were able to restrict the amount of implant-devices in your surroundings (it is rumored that extremley rich people is able to block external signals and have a strict control of devices operating on those frequency -including the implants of their own employees-). However, that's not something that is achievable by an individual, as that spectrum would be used anyway by your neightbours' devices. You are facing a tragedy of the commons that killed the implant era.

Who cares?

No-one reading your story actually cares what the reason is. What we care about is the story you tell about the consequences. The reason is a MacGuffin which doesn't have to exist in any defined way.

Think of the classics. You don't need to know how Victor Frankenstein connected up the nerves and blood vessels, only that he did, and this is how his creation behaves. You don't have know how the Dune Navigators figure out piloting, only that they do. You don't really care how the Snow Crash Burbclave residents make money and how the Burbclaves negotiate, only that they do, and this is how their society works. Or even closer to your scenario, the post-human Machine starts to break down, and the post-humans have to work out what to do when The Machine stops, but no-one needs to read about the detail of the Machine's repair procedures.

The tech stopped working. Post-human has to work out how to become human again. That's a brilliant hook for a story I want to read when you're done. Why it happened is unimportant to the story - give me the most basic Scotty/LaForge handwavey bullshit if you really want, and move right along.

The biologicals are not actually still biologicals.

The entirety of human civilization was copied and continues to run as a Matrix-like simulation. The event 5 years ago was actually the first boot of the copy. Failure of the implants was intentional and meant to distract from other imperfections in the copy.

The fate of the biological originals is not clear - maybe they perist and do not know about the copy, or maybe they were wiped out, or maybe (again like Matrix) they are being put to another use.

As I see it, for the effect to be quite sudden and global, there are two options

1) outer influence, new kind of radiation, aliens, gods, magic appearing out of nowhere you name it. Generally not very plausible, but there are stories set in worlds in which such a game-changing event occurred. If the setting is interesting enough, the question how it came to existence can be handwaved to an extent.

2) something contagious

2a) some disease/virus. Not very plausible, as generally any change in brain chemistry/structure so strong that it affects implants in an irreparable way would probably be conflicting with normal brain function way too much.

2b) some kind of mass hysteria.

I am imagining this scenario: A new implant was created not long ago, maybe something directly influencing mood. Basically everyone got one, because it was cheap and sooo handy. Unfortunately it was not tested thoroughly enough. After some years of use it causes not only irreversible changes in brain chemistry (that might be easy to cope with, you simply adjust old implants to this change), but unpredictable fluctuations, peaks, rapid changes thereof, so basically any adjustment you make to any of your implants will let it work for an hour or half a day before your brain fluctuates out of sync. When this happened to the first affected person and the news spread, other people soon became scared (back to mass hysteria point), which significantly strenghtened the effect up and sped up its onset. Eventually this panic caused even those who haven't got the original faulty implant to become affected. Check out wikipedia on mass hysteria and imagined illness.

Not sure if it makes much more sense than alien force field, though.

Go for the simplest solution: millennium bug.

You would think that humanity would have learned after Y2K. Nope. In another post I described how GPS has a millennium bug every 19 years or so. This is due to a design flaw, and the fix is people having to buy new GPS devices every 19 years. We are now in the first generation of devices which may survive this because cell phone apps and OS's are patchable for this, but a lot of standalone GPS devices did go nuts on April 6, 2019 and are now useless. The next time this bug will hit will be around 2038.

---

So it may be that your biotechnology devices have an embedded millennium bug in the firmware which everyone forgot about because no one cared. Maybe fixing it would be too expensive, requiring everyone to change their parts. Every corporation was waiting for someone else to invest the time and money to fix it. This went on for long enough that the risk eventually faded from memory.

Now no one knows how to access firmware, and thus it can't interface with flesh anymore.

By the way, a simple fix would be to reset the date in the devices. Unfortunately no one knows how to do that.

Although the question is open ended the answer is far more limited. No matter what, it has to be the biological connection to the mechanical part that prevents a good interface. The mechanical part can be adapted to interpret the nerves again, but if the nerves can interpret the mechanical part the system fails. That limits the options to anything that changes the neurotransmitters or the nerve itself.

A virus that causes neurological damage is out of the question, it would not just kill the interface but also the connection between your own nerves and kill you or severely handicap you in the process. This also means that anything affecting the neurotransmitters is out of the question too.

That leaves the nerves themselves. And the only option they have is to either grow or reduce in size. This growth or reduction in size severs the connection to implants in a short time causing the implants to fail, and failing implants are likely painful if not dangerous for the wearer.

The best culprit is an evolutionary chain towards regeneration. People will need surgery for implants and as the population increases that has had to recover from more and more invasive surgery a selection process begins towards better biological regeneration. People with this better regeneration have less complications after receiving implants throughout their lives increasing their economic and social standing and chance to have strong babies themselves. Unfortunately this has caused a string of dead-end evolutions that included nerve regeneration, which does not have to grow back correctly. The surgery causes the nerves to undergo rapid growth to "repair" the damage not knowing that an implant has taken the place of the damage. This DNA string was first faulty near the end of people's lives where the higher risk of complications made it less noticeable but a trigger has caused it to start expressing itself in most of the population.

• Change of diet: the implants need some chemicals/proteins/etc. to work, or to be able to interface with your biology. Something wiped out a kind of a crop, that forms the major part of your societys diet, that was the only source of this protein. Or the opposite, some company introduced a new soda, that became such a big hype, that almost everybody tried it. It took some months/years for a compound of this soda to render the interface between implant/biology non-functional.
• EMC: there was a major electromagnetic event (solar storm, terrorist EMP, name your thing), that went unnoticed by your brightest or swept under the carpet by the government. (Or a radiation event, like a few weeks ago in Russia.) Your implants do not have electromagnetic shielding, since it would make them look worse/reduce their usefullness, they were more sensitive to this event than your normal devices. Or this event was frequency selective and only your implants were sensitive to it.