Paul Mccloud

Happens to me too, not sure what it could be. I Afk-ed at my mob farm (which works about half the time) and for 8 hours there were 0 spawns. The light level is 0 and it's 250 blocks up in the air. I Afk-ed this afternoon and perfect rates. It's on a realm and I have no idea what is causing it.

Just had the same bug, a level 3 librarian with good trades changed to a toolsmith. The toolsmith was also leveled to level 3. I am using a Zombie spawner for a zombie cure discount, but I'm certain that this villager was not originally a zombie as I named those to keep them from despawning. I have not been able to reproduce the bug, but I did break the lectern as soon as his first trade was locked which is so far my only lead. what was confusing is he only changed profession immidiatly after I placed a grindstone. I don't think this should be a top priority, but this bug was certainly frustrating. Honestly, I don't even remotely know what could cause this bug but here's my vote.