Neutral and ground can only be bonded together at the service entrance point. For a RV that would be at the shore power main breaker at the shore power source, not in the RV. It would also be at the coach's inverter and generator. This is why the transfer switch and inverter's bypass must switch the neutral line.
You need to use a voltmeter to read between L1 and ground and L2 and ground at the shore power connector where you plugged the coach in. If voltage is there, then you do not have an open ground. If there's no voltage reading, it's a shore power problem.
If the problem is not the shore power, measure as described above, at the sensing circuit board. If there's voltage reading then I need to know where the circuit board is wired; before or after the transfer switch, before or after the RV's main breaker panel?
99 Country Coach
Prevost XL 45 Conversion