So, I've been playing on a private server with some friends and managed to create a villager trading hall with an automated curing system. After some time I realised some villagers forgot their discounts (zombie curing discounts) for some of the items, as can be seen in the librarian. Tried to cure the villager again but it only solved the problem temporarily as it has reverted the price of the books again.

Also noticed this other villager that increased the price of some items and decreased others after some trading instead of lowering them all. Really weird stuff