I would open the breaker panel and check that all hardware is tight but before you do unplug from shore power and trip the breaker(s) on the generator to ensure ALL power has been removed. Do the same for the transfer switch.
A loose clamp holding a wire feeding power from a breaker or the neutral bus bar could cause a low or no volt situation. Cycling the breaker might have moved everything a bit to get partial power. Running the convertor off a second outlet is an OK short term temporary solution but best to have it on a dedicated circuit. Draining the house batteries and not being able to recharge makes life in a coach difficult considering how much stuff requires 12VDC either as primary power or for control purposes.