If the battery is low on charge the converter can draw around 1000 watts. Microwave will pull 1500. Fridge 350. Water heater 1400. Coffee 800 to 1750. Electric cooking will also draw 400 to 1000 watts each appliance. Some of these run on a thermostat so it could seem random when the overload hits.
So you may need to give your converter an hour to charge the battery before you crank on the A/C. Otherwise watch what else is plugged in.
Also if you are at 4000+ feet altitude your generator will be derated some due to the thin air.
I doubt the #10 extension is causing any meaningful issues.