Just put ours together (bought and built at the end of 2019, 10 months after Ian’s post) and had the same problem. A few keys do not work unless you also touch the battery’s metal case which implies that the code doesn’t auto-configure the key’s capacitive settings (hard coded?) or there’s an issue with the auto-configure (if not hard coded).
Probably would be resolved if the board is installed in a metal box and you held the metal box while using.
I noticed that the resistors connected to the different pads are different (high) values. Do they need to be tweaked to get this to work?