Villagers will randomly despawn with no trace. They have beds and work stations and they're confined in small places while it's on peaceful and they'll just disappear. There is no logical reason for them leave and it's annoying. I have a town with 50 villagers on the dot and some just randomly leave. Again no reason for this to happen and it's a fixable bug. This has happened on multiple worlds too. This has been here since the release of 1.17.