A stuck button could cause strange unpredictable behavior. Make sure it is not in a case, nothing pressing on buttons. Is there a screen protector? These can affect the touch interface.
Further troubleshooting, simplify down to the most basic configuration to reduce the possible factors.
- remove all non essentials, like microSD card.
- download fresh copies of the stock FW. Download from another PC. Make sure you don't have a corrupt copy of FW.
- Reload stock FW multiple times. This should have no theoretical effect, but there are observations that this restored the original SQ. You are in a state where grasping at straws is allowed.
- try another cable
- try a Format System Storage (backup first)
- Use only the internal memory. Copy a few new songs onto the internal memory, and observe. Get it back to as basic a configuration as possible, and see if the problem is still present.
So some things to try.
Edit: Older Stock FW locations.
https://walkman.update.sony.net/fw/pc/WM1/NW-WM1_V3_01.exe
https://walkman.update.sony.net/fw/pc/WM1/NW-WM1_V3_00.exe
https://walkman.update.sony.net/fw/pc/WM1/NW-WM1_V2_00.exe