Can you trigger each switch in turn and see which indicators light up on the diagnostics screen? I assume that these Mx indicators map to the notional 6 axes that Mach3 can handle but why they have not picked up the usual X/Y/Z etc labels I don't know.

I switched to UCCNC on both my CNC machines so I can't replicate this screen, unfortunately. I had been using Mach3 with an ESS but had problems with it so swapped to a UC300 and UCCNC - but not the same problems you are seeing.