It's not just skill books, either. I've had almost my entire inventory, including equipped items and quest items, completely disappear randomly when I get into a fight or talk to people. I have to reload a previous save to get everything back. I'm starting to think I'll have to save before *every* fight, just in case this happens again. And it really sucks because, being an Undead, losing Fane's mask means everyone knows and wants to fight me.
This is a good game, overall, but Larian *REALLY* dropped the ball with this issue. I've seen where this has been happening since the Beta release, and here it is in 2021 and it still hasn't been fixed. I've already had to start a new game and remake my character, because the character I was playing before lost almost all his buffs. I don't know if this happened previously, or if this game-breaking bug is a recent thing, but it's incredibly annoying to have to 'save spam' like this just to get my items back.