Hhmmm, now this is interesting. I decided to put the known good board (from the original key) into the better-nick new key, and keep the rest as a spare which could probably be kicked into life if I ever lost the one I’m using.
And… the problem stayed with the new case, not with the suspect board – I’m wondering now if the newer case has worn in a way which lets it flex or something, stopping the buttons pressing the microswitches hard enough? Must admit I don’t find that explanation convincing, but not sure what else to think
