Generator stalls & main 12 volt circuit breaker trips

12v main circuit breaker ?

you have 12v power, until you start the generator ?

then this 'breaker' trips and everything goes black ?

are you on shore power ? how are the batteries charged

yes .. there is a load, the converter will come on as soon as the timer on the ATS kicks in, also possible is any switch that might accidentally be on, like water heater or fridge
a bad converter or two many items in the on position, will cause a small generator to stall, 2800 is NOT a large generator