This has actually happened to me twice now. I have a bunch of villagers in a trading center, but a bunch of them have suddenly disappeared. I didn't see them disappear - one day, when I went to see them, they just weren't there. I thought it was just one-time thing, but it happened again today, and it's really frustrating.

I didn't think villagers could despawn (although maybe I'm wrong), so I'm really confused as to why this is happening.