Master Level Swamp Cleric became No Level Normal Farmer

My trapped Master level Cleric, a swamp biome villager, suddenly became a normal villager with no experience/level. This has really messed things up for me and I cannot find anyone who has had this same issue. If anybody can help in anyway, it would be appreciated. But things like this take away MASSIVELY from the game, I've had this world for nearly a year and I'm about to be done playing the game entirely if I can't even rely on my villagers to stay the same.