There should be no continuity between the neutral and ground. Check power distribution panel for connection.
The DC and AC ground are the same. Both should be connected to frame of the rig.
Turn off all circuit breakers in the rig. Check at AC panel for proper connection to shore power. Test using Ohm meter with power cord unplugged from source. Check between each conductor for any resistance.
Plug rig back in with all circuit breakers in rig shut off. Turn on main, check for issue, then turn on each branch breaker one at a time. to identify which circuit has the problem.
It could be bad refer heating element of bad 120 volt heating element in water heater.
Conversion from 30 to 50 amp? Has any work been started and why?