Lots of resistance on shifter when engaging any gear from a stop; not an issue if clutch pedal is depressed for a few seconds

2019 Mazda MX-5 M/T, 16k miles, original M/T fluid.

TL;DR (I originally wrote everything below the TL;DR and then realized how long this was…):

• When not moving and depressing the clutch, all gears are hard to engage (feels like a notch I have to push through) if I try to engage them right after the depression. This is a relatively new issue in a car that’s 2 years old.
• When not moving and depressing the clutch, if I wait 3 seconds with the clutch disengaged, all gears are very easy to shift into.
• Pumping the clutch a few times before trying to engage a gear does not seem to help.
• It does not appear to be a fluid temperature issue, since even 45 minutes into a drive with plenty of stops, the issue was consistently there.
• No issues engaging/shifting gears while on the move.

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Longer version:

It has become very hard to engage any gear from a stop when first depressing the clutch pedal, i.e. in the timespan right after the disengagement. It feels like there’s a notch I have to push through. I’m not entirely locked out, I can push through it, and after that all gears are super easy to engage. At first I thought it was only 1st, since I normally don’t try to take off in 6th from a stop, but I verified that it’s all gears once it was suggested I try that.

Engaging the clutch while in neutral at a stop, even after I’ve successfully pushed through the notch into 1st, and disengaging it again without waiting much, causes the issue to immediately reproduce.
Meaning: Depress clutch pedal, fight through notch to engage 1st, smoothly shift between any all gears after the first engagement, back to neutral, release clutch pedal, depress it again right after, notch is back. Rinse, repeat. As long as I release the clutch pedal, each time I push it back in, the first few seconds all gears are very hard to engage, but not impossible.

No issues shifting between gears while on the move.

The original suggestion from MX-5 forums was the M/T fluid, since it has helped a lot of people on there resolve notchiness when engaging gears.

However, a local trusty mechanic’s theory was that it’s a clutch hydraulic pressure issue, and he had doubts that changing out the M/T fluid would do anything. Since the car is still under warranty he suggested that I take it in for diagnosis and repair under warranty before I have them (the local shop) try repairs out of pocket, so I’m looking for clues and advice to take to the service advisor and takes on Monday (1/25/2021).

It was suggested to me from someone else that I try pumping the clutch 3-4 times and then try to engage 1st to see if it makes any difference. If it did, it’s minuscule. But, in the process of trying that, I thought about holding the clutch pedal down for a few seconds (say, 3 or 4), rather than trying to engage 1st immediately after depressing it, and what do you know, the shifter goes into gear buttery smooth. So, push clutch pedal in, count to 3, try to engage 1st, buttery smooth.

So the current running theory is a pressure leak in the clutch master cylinder or some other related part of the system, since the issue returns every time the clutch is engaged at a stop, even for less than a second. The clutch is hydraulic and shares fluid with the brakes, and the fluid level was at full.

The pretty stark contrast between smooth engagement and the hard notch, as well as the consistency of reproducibility of the issue leaves me relatively confident that I will be able to have the Mazda tech reproduce it as well, instead of being waved away with "this is normal". But, like I said, I want to go in equipped with as much information and suggestions as I can.

I’ll admit that since I’ve mostly been driving on backroads once a week for the months since the pandemic started, I have no idea how long this has been an issue. Not much coming to a full stop when you’re out on the coast or in the mountains. Pre-March 2020, stop-and-go traffic in this car was an almost daily occurrence, and there was definitely no such issue with such frequency. 1st would be hard to engage maybe once every 100 engagements or so, but I would just slip it into 2nd first and then 1st, or just push through the notch anyway.

Appreciate any and all theories as to what might be wrong here.