For some reason when i cure a villager i do get the discount but no matter how many more times i cure the villager the discount on the trades dont change, this applies to at least 4 librarians, 1 farmer and 4 clerics i tested with doing multiple cures each. The discount works just fine on singlepalyer, is this a config i dont know about?
The serve is a paid bukkit server running no plugins but running some datapacks wich i dont know all about. The ones i know are creeper grief and enderman grief protection, multiplayer sleep and fast leaf decay from vanilla tweaks, but there might be more datapacks.

Just to be clear with an example, if a cleric buys 32 rotten flesh for 1 emerald then i can cure it so the price drops to 26 rotten per emerald, if i cure it a second time the price drops to 20 rotten per emerald (as tested on singleplayer), but in this server the price locks at 26, that happens no matter how many times i cure the villager.