Finally found the solution:
The default configuration of GPIONext is not optimal for those inputs.
What fixed it:
Hope it helps someone else !
@mitu Just yesterday, to get the latest binary. I'm going to try and do what it said in that post you linked me to.
Its not removing any configuration the devices are named the same what you need to to is wire them up the same and you only need to set it one time will work for both players as its configured per device.
It may have changed something because when I try to plug in the keyboard after starting the game with it unplugged, the keyboard doesn't do anything.
There is a new input mapping screen starting with RetroArch 1.7.2 - https://forums.libretro.com/t/new-input-remapping-menu/15584 - and as a consequence the previous re-mapping files are not working. I think that's what you're experiencing. Can you give more details about your system - as requested in https://retropie.org.uk/forum/topic/3/read-this-first ?
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