Please answer the earlier questions that would help pin this down:
1. with no shore power, does the inverter work ok?
Note the inverter must have 12v from battery to work at all, AFAIK. I don't know if the 120v CB on it is "popped" with no 12 power to the inverter (thinking how a GFCI will not reset unless it has power)
2. With no shore power do your lights and fans work? So we can say the battery 12v is getting to the DC fuse panel or not.
Can relate to 1. whether the inverter is getting battery 12v.
The inverter would have its own transfer switch that could be checked. Not to do with the coach's own transfer switch between gen and shore power.