Inverter
Sounds to me like the inverter failed. When you turned on the generator, the converters' transfer switch disconnected the 12V from the batteries and then the converter was not delivering it's 12V power to the 12V system. When the converter was de-energized, it's transfer switch was also de-energized leaving the house batteries to power the 12V house loads. You better charge the house batteries from either the engine or an external 12V battery charger before they are discharged beyond repair/rechargeable.
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