The Honda in Eco will "surge" engine according to load. You are reporting on DC amps from the converter going up and down, which is not the Honda--except with less converter load it will not be as loud.
You could eliminate the Honda confusing things as an issue by doing it with no Eco.
So the question is why are the converter's amps going up and down? Something funny with the acceptance of the batts? LFPs ISTR, so might be something with those, can't say. (balancing?) But then you would be at a higher SOC than stated. Monitor not zeroed? Then it steadied. Balancing all done and now just any loads present? Not enough info.
