Indication is park has an open ground.
I get that on generator (For good reason) but not on shore power
Try this. I carry a FULL range of adapters. 15-30 40-50 and the other way around. I can basically plug anything into anything RV wise. Using a 15 to 30 and if needed a 30-50 plug into park. If you still see OPEN GROUND notify management.
Regarding 60 volts hot or neutral to ground. NORMAL if you have an open ground.. I can explain why but it's a bit technicial.
Basically the cables (Romex mostly) in the RV from what is called a capacitive voltage divider and 120/2 = 60