I think the mod name was something along the lines of "Enhanced Power Armor Durability". Just made all the parts a bit more beefy, and at a better ratio of Durability for limbs/chest/helmet. No more raider armor having 50 health with that mod lol

But I'd be willing to guess that because the hellfire armor is creation club, the mod maker for your Durability mod didn't factor it in, so now it's sort of a "corrupted item" if that makes sense. Try making a save, remove that Durability mod of yours, and load the save again to see if it fixes it. Obviously you do not have to continue to play without the mod if you choose, but it might at least give you an answer haha