Controller shutting down/disconnecting when shaken/moved around

Hello! I have this controller for 2,5 years. It's working flawlessly in all regards except random disconnections/shutdowns.

I use it on PC, wired, no batteries inside. When it's just connected or I play relatively calm game where I don't move my hands around much it works just fine. When I play something intense like fighting game where I move my hands with controller around (this is due to execution demands, like frame perfect inputs, motion inputs, combos, can't be avoided) it disconnects, or shuts down randomly.

I did some troubleshooting, tested it with batteries via bluetooth, also disconnects. Tested different cable, also happens. Tested on different PC, also happens. Plugged it and just shaken it around violently (but of course not to damage it) and it happened, on both PCs, bluetooth or not, cable 1, cable 2, cable 3. I also updated controller's firmware. Nothing helped.

Disconnects or shutdowns? When it was connected via cable it seemed like it's losing connection, but when I used it via bluetooth I had to pair it again (holding the connect button on the controller was required, then it paired with PC and then I had to hold xbox logo down and it was working again), while via cable it resumed working after 2 seconds or so.

I suspect it must be something inside which is scary in itself, but I don't even know what I would need to look for inside when and if I manage to disassemble it. Does anyone have an idea what could be the cause and possible fix?