Problems upshifting with 105 5700 derailleur w/ Roadlink

Question

I found a similar question here but no practical answers, wondering if anyone has encountered anything like this.
I have a 105 5700 long cage rear derailleur with Roadlink extender installed and an 11-34 cassette.
When downshifting (from smallest to largest sprocket) I have no problems, but when upshifting the derailleur skips a gear twice. In other words, when in the lowest gear, I shift once and nothing happens. Shift one more time and the derailleur skips the previous gear right away. The derailleur itself moves as it should but the chain stays on the previous sprocket.
The derailleur and the hanger are straight, the cables and the housing are new. I have a 38T narrow-wide chainring in the front.
Here is a sketchy diagram that shows which sprockets are skipped:

I couldn’t come up with a reason for why this could be happening except that the difference in the number of teeth in the lowest gears of the cassette is simply too big for the derailleur which worked just fine with a 12-28 cassette before.

Nathan Knutson · Answer

That is the shift where having too much b-gap can cause the exact problem you describe, and the Roadlink is there to artifically increase the b-gap. It may not be solveable, and if it is then getting the b-gap as close as possible while in the large cog is likely going to be part of it. The caveat here is that if it's close enough to grind or touch, that can also make the shift lag.
Wear to the RD pivots and pulleys will make it worse because it decreases its ability to pull the chain assertively. Likewise the chain being worn could in theory make this problem worse, but not necessarily to the extent that a new chain would fix it.
If the setup was working and now suddenly it's not, pulleys would be the easy thing to look at first. 5700 doesn't natively have very much pulley slop at all, so if you find the guide pulley has much wiggle to it then you may be able to fix it with a new set.
If you had a way of increasing the return spring force, that may help solve the problem, but 5700 isn't built to make it adjustable.

Problems upshifting with 105 5700 derailleur w/ Roadlink

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