Hi, peteb2 suggestions are fine. So, looks for some dirt, bad connection on pin header X13 and IC19 (you can try to resolder all pins). I've tested all boards (100%!) one by one, on my test configuration and all passed basic testing, i.e. firmware selftest procedure. It's also possible that X13 is not cleaned up properly. This is definitely not a firmware bug, because all boards are preloaded with (now obsolete) v1.0 that works fine.