Trigger button randomly pressing. Took the controller and pads apart

Once you open your controller and take out the motherboard, you can see the flat cable that all buttons are connected to. Make sure that the contacts are fully clean, both on the cable and the motherboard itself. Use some rubbing alcohol(isopropyl alcohol or so) to clean it, as water may damage other components.

If that doesn't work, you could try to replace the flat cable and see if that works.