timppu: I don't know if it is the same problem, but I've had two of them since start of January. They've been mainly been used by my two sons with Nintendo Switch.
One of them feels as good as new, while the other one has its upper right shoulder button (the non-analog shoulder button) lose its feel, ie. you can't really feel when it is pressed down and when not.
The button still seems to work fine (ie. when you push it, it is activated in the game, and when you release it, it is not), but now it feels almost like a touch switch since the travel of that shoulder button was so small to begin with.
That seems the problem I described and in my experience, the L1/R1 shoulder buttons are the first to go. In my case it was caused by intensive use, I play a fighting game that need to press R1 button constantly. It seems L1/R1 are the worst offenders and the A/B/X/Y hold quite a bit more. After some more use the buttons don't recover to the OFF position.
For the buttons they use the silicone rubber diafragm type, like non-mechanical keyboards and the diafragm start to crack eventually.
Note that most controller I've used, don't hold up a lot of time playing fighting games so not sure if it's a issue with the 8bitdo in particular.
I've asked 8Bitdo to buy replacement parts and they sent me a kit free of charge. Since this was at the start of the pandemic, the kit took 2 months to arrive. Due that time, as a temporary solution I've inserted a small O'ring under the worst button, since the lack of feel made me press inadvertly the button.
Since they don't even asked for a invoice or date, just a photo of the controller to check the model, ended buying a 8BitDo Zero soon after due they service.
timppu: EDIT: Also some of the analog shoulder buttons have occasionally popped out when my kids have dropped the gamepads, but they can be easily snapped back into place. Apparently those shoulder buttons can be easily popped out by just pulling them out anyway, apparently by design.
That is the way they are designed and to disassemble the gamepad they need to come off.
