You need to know what the power at the pedestal, where you pulug into 50amp Is the first place to look. We were plugged into 30 amp recently and watched the voltage drop to 106! It was heading for 90 deg F (33 C)and the utility had reduced the voltage in a Brown out.
With 50 amp at 120 volts I can run two a/cs, microwave, and coffee Brewer with no issues.
As others have said, check the power you are receiving then follow the power into you coach through the inverter. When you find the low voltage you have the source of the problem