You could also check your ground daisy-chain to make sure they are fully connected from the 1st button to the end button in your chain. Also if you press F4 out of emulation station you can test all your buttons in the command line if you're using a zero delay encoder or something similar.

@simmy Hello i too have problem with 3H arcade 2Players controller. up and left not working. One think i can manage is to have 2 players configured. You need to insert at the end quirks line in /boot/cmdline.txt file. :

usbhid.quirks=0x16c0:0x05e0:0x040

This entry enable 2 players in retropie.
But unfortunatelly left and up is not working at all.
In recalbox and windows everything works ok
I have found some info in this thread :
https://retropie.org.uk/forum/topic/4361/20-pin-xin-mo-wiring-diagram-set-up/7
Maybe this is a solution.
I cannot test it right now. Can someone test if changing pins can help ? Is P1 & P2 sides of the board Pin 2 and 4 are dead. ?
Any help ?