Also, AC power enters the load center via the automatic transfer switch. Possibly a problem with this switch?
Also, AC power is distributed through the breaker inverter panel that is mounted adjacent to the main load panel. Either inverter power or AC power from the park post is feed through this panel and distributed to outlets.
AC power needs to be traced back through these panels to determine where it is or is not available.
You can see this electrical design on schematic titled wiring diagram - body 110V.
Hopefully the above will be able to give you a clue to solve 110V power loss.
'10 Phaeton 36 QSH-