That does help. I reset it, and reviewed the manual. It does state it should prioritize AC supply. (of course just like the CFX40 manual, it also says not to plug in both cables despite advertising the feature)If it helps, I can confirm that the CFX3 75DZ does indeed shunt to AC power when present on mine.
It seems to be working now. Watching the meter it seems to handle the hand-off back and forth from DC -> AC , and vice versa less smoothly than the old unit with some voltage spikes. I'll just start using it as intended and see if problems arise.