I added a strength +2 charm to a helmet in Jackson dungeon. My first attempt at charming something. I was not sure it actually added +2 strength because I didn't check to see what my strength was beforehand, so I reloaded the same save point to retry it and the charm is gone. Nowhere in my inventory. Tried old previous saves and it's not here either. Is this a known bug? Thanks

I have not seen this reported before. You found the charm before your last saved?
The only issue with charms I recall is that they must be in your inventory to use, not in the battle tower chest (which obviously isn't the problem in this case).

If you select the helmet and try to charm it, do any charms show up in the list?

After adding a charm to equipment, it shows up in the item description (the 'empty charm slot' icon and description are replaced with those of the charm).

It all worked fine when I initially charmed the helmet. I found the charm before my last save. The other charms I have show up in the charm list when I try to charm the helmet, just not the strength +2 charm. It just disappeared after I reloaded the saved game. But yes, the charm was in the inventory of the saved game. Now it isn't even in old saves - it's just gone.
1) - load up a game
2) - I'm in the dungeon - wonder what cool charms I have?
3) - I need strength - I will put this +2 strength charm on my helmet. Been lugging it around for awhile anyway.
4) - cool it went on! - wait.... did my strength actually go up? hmm, I better go back and retry that and make sure (turns out it did)
5) - reload saved game at dungeon and click on helmet to try charm again, while noting current strength - hey, where did it go? It's no longer in my list of charms, and not in my inventory?
6) - try to load game before dungeon to see if charm is in inventory - not there

Bummer - I was hoping someone had a similar experience or solution. I love the game, but when stuff like that happens, you always have that nagging feeling of "when is something like that gonna happen again and mess up my game?"