Okay when I simultaneously press a different button then the two that are connected to header P5 (gpio 30 and 31 and ground 1 en 2 of P5) and one of the buttons that are connected to P5, that button ‘fires’.
So It looks like gpio 30 and 31 one are not reacting to the grounds of header P5 but to the ground op the main header P1.
I checked my wires but there are no lose connections. And when I install my sd card with the old retropie, the buttons work? So I’m pretty sure its not a hardware problem.