I have an entirely survival world with no cheats, and I worked hard to get my villagers. They have been part of my world for a while. First, one villager disappeared, but I didn't see it, so I thought maybe a mob killed it, even though the place they are in is really safe, and I play in peaceful half the time.

Then another disappeared, but I saw it happen and ALT- F4ed out. I managed to save it.

I log back in to check, and within a minute, it happened again. THIS TIME I SAW THEM DISAPPEAR. (B4 I'm asked, yes they had beds and doors.) I tried to ALT-F4 again, but when I came back in to check, they weren't there. I had two more, so I thought I could restart the breeding process. Even though it took me forever to get me the villager trades I wanted the first time.. Mending and Unbreaking 3.. but then POOF! the last two villagers disappeared off my screen. I am ready to cry as I had spent a lot of time on this world.. Please help. There were more than enough beds, and there were doors close by. Three of them that vanished even had nametags on them.