you may simply have a loose wire somewhere, which works 'most of the time', until a sudden rush of heat caused by a high-amperage device - such as the microwave...
it can exists at the power pedestal itself, the shore cord, your ATS(auto transfer switch)box, or your Main Breaker panel... many new coaches experience these issues from the factory - the workers 'tighten' the wires initially, but when in 'real world' use, they can move slightly and cause issues until tightened again.
To really 'check' the status of voltage at any source, such as the shore power pedestal's main breaker/outlet, get a simple 'volt meter' at the big box store, in the automotive or hardware area, or an auto parts store. Turn it to 200a(for voltage up to this amount) for AC, turn on the unit, then put one lead into one of the HOT legs, usually on either 'side' of the 50amp outlet, and the other in the NEUTRAL leg, usually the bottom.
This should give you something like 120volts - or around that number since it varies.
You then do this again but only move the left HOT leg to the other side's HOT leg of the outlet, which should ALSO give you a similar number.
If both of those are giving around 120volts - which is 240volts for your RV, then it is working properly.
You can check your other parts the same way. You'll find that 240v power is what is coming into your shore cord, into your ATS, and then into your Main Panel, where it is then normally 'split' between two 'sides' of breakers, each sharing some of the 120v power on each side, up to 100amps, total.
'14 Thor Palazzo 33.3 compact diesel 110k+miles since '14... US, Alaska, Canada...
AND a '14 Gulfstream Amerlite
AND a '07 ForestRIver Rockwood