I had 3 villagers transported to my home, and they were kept in minecarts. I just left them with no trades, etc because I didn't have anything to do with them at that time, and also wasn't ready to build a trade hall. And I played for hours mining, and I found out that they were missing. This bug seems to have been reported in other versions, but it seems to have occured again.

Edit:I told this to the server operator, and he said they might have been killed my zombies, and he would check the log as fast as possible.
Edit: They were killed by zombies.