IIRC you have done power factor and load tests
But I don't remember what the VA and PF were
I think You are hitting the limits
Cooler temps mean higher charging voltages for lead batteries (AGM is lead)
When you did the power supply test, supply voyage was lower, the battery was under load, the combine converter & battery voltage level was probably barely above 13v maybe less
13*75 is less than 14.× * 75
Which means a different VA loading on the generator
92 Oct non ethanol may help, warmer weather may help
A bigger generator or smaller charger WILL help
