Post count: 10

2 Things:

1. How are the Arcade Cabinet Controls setup, whether USB or GPIO?

2. That seems a bit weird to me that a controller would be plugged into a cabinet, but it sounds cool.

But it seems to me that you are using the RetroGame library from Adafruit, which can handle input from the GPIO pins via keyboard presses.

If that is the case, make 100% sure that the setup for Player One in MAME is Keyboard Only(AKA configure it so that there is not mention of Joystick 0).