I have a newer model RetroDuo that was working fine for a while. However, recently I have been experiencing a really odd problem. Whenever playing a two-player simultaneous game, the game will constantly pause if both players press two buttons at the same time (A, B, X or Y buttons). Does anyone know why? Has anyone else experienced this? Any solutions?

It is absolutely not the cause of the carts themselves. I have tested them on an authentic SNES with no problems to be found.