Not sure if your still doing bug fixes but i encountered one where my HP stays at 1 but I can't use it, the NPCs treat it like I have none. I still get full HP every day and if I have 10 I can still work two 5 hour shifts but it stays at one, but if I have 11 HP and work two 5 hour shifts and should still have 1 HP left naturally I also can't use it. I tried going back to an earlier save, starting a new game and redownloading but so far the problem is continuing, so for the most part I'm starting the the game out with 9 HP since most evening activities cost 1 HP. I think it started around when I got my first extra HP from Stamina because I did a run before where it was working normally.
It's been a while but I went ahead and gave this a go and tested a few things out. This is due to software limitations of rpg maker software. Unfortunately, you cannot spend the 1 HP and in this case it's treated as a replacement for 0HP. Usually reaching 0HP means the character will die and the game will reset (This is just how the RPG maker software logic works).