Villagers stop gaining experience

My villagers have stopped gaining experience from trades. A couple of them do show some experience, but now when I do trades they do not appear to gain any experience. So it looks like they started out gaining experience, but for some reason have stopped. 

The world was created with  the 1.19.80.20 preview, and I'm still using the same version, so it's not something that stopped working because of an upgrade tp the game. 

I'm not sure what your policy is re: uploading saved games, but I can do so if you would like.