What sort of outlet is the rig plugged into? 15-amp or 20-amp "regular" outlet? Or is it a 30-amp or 50-amp RV outlet?
If it is a 15 or 20-amp household outlet, is it a GFCI breaker or just a regular circuit breaker? If it is a GFCI, it is not uncommon for the shore power GFCI and the onboard GFCI to have a "conflict" and the shore power GFCI will open and cutoff power.
If it is a traditional breaker opening what items are still turned on in your coach? You might try turning off the rig's breakers, except for the "Converter" breaker. Keeping that breaker turned on will keep the rig's batteries charged, and you can see if that allows the shore breaker to stay energized. If that indeed works, try turning on the other breakers until you find out what circuits trip the breaker.