I don’t know if this applies to the Isata, but if you have an electric fireplace and you are using it, there could be (some sort of) a switch that automatically turns one off while you are using the other. I know a lot of 30amp RVs are setup this way. Again, no idea about your RV.
2016 Rockwood Windjammer 3029W Diamond
2015 Chevy 3500HD LTZ 6.0 Crew Cab 4x4 Long Bed 4.10:1 SRW