Crazy 'nothing' to consider... What if there were some insulating material on the board or the keymat - or if the keymat were just a bit out of alignment (no alignment pins remember) such that the keymat isn't making correct contact for the non-working button?
The keys don't even work when the board is removed and I'm manually making the contact with a special tool we built back in Pandora times (basically a tip with a carbon pad on top).
Nope, it's not a contact issue.
Or check it's not some weird software definition issue before cutting into keymats. A lot of this is up to what is defined in the device tree binary.
That would affect all units, not just a few boards with different keys.
Yeah, I can't see how a diode can be reversed in a modern production routine, unless it's backwards in the intial schematics.
Oh, they sometimes are reversed inside the reel even. I had a few Pandoras where some LEDs were reversed and didn't work
The more tiny things get, the more stuff goes wrong.
It should be easy to see if the diode has been misplaced, and is only held by one pad or entirely missing now. And even 20EUR multimeters these days have diode testers in them, so if you can physically get at the contacts to the part you can test its orientation fairly easily.
Diode testers only work reliable when the diode are removed from the PCB. You can't see if a diode is reversed, as these are about 0,4mm x 0,2mm parts... you won't find markings.
Yes, if one is missing or misplaced, you can see that, which is what Nikolaus will do. I don't even know where the diodes are on the PCB
And no, it can't be a software issue, as all units would behave like this in this case.