I have had librarian villagers that were traded with, leveled up to past 3 for most of them; name tagged and all had access to their work stations and beds trapped in a house disappear twice now. This was never an issue pre 1.16 - the first time it happened was two days ago and only half of them disappeared so I gave them some carrots so they would reproduce and they did. I swapped the lecterns till I got the trade I wanted and then name tagged and traded quite a few times with them. Came back today to check on them and all but one of them have disappeared again. They're trapped in a house that's well lit, they can't get out and there's no way for them to die.