I got super nosey about the answer to this. I am not a controller expert, but it sounds like you need to do some more teardown. Most of the signals for buttons are carried by a huge flexible sable that surrounds the frame the board is attached to. This is a picture of the front part of the trigger. The blue cable is what ultimately sends the button signals to the controller's board. It could be something isn't quite aligned properly, or the cable is damaged.
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