Once it gets below a point, the game doesn't let you restore them to the starting and out of combat max.
Does this happen from certain status effects or as a result of those?
I don't know what to tell you that the file doesn't. I don't do anything speashul in combat or that anyone else doesn't do in "danger" areas. Only save edit I remember is freeing Reaha without losing her. I hope someone fixes it in future builds because it gets really dangerous on Phadera.