Villagers are disappearing

I have a breeding room with lots of villagers and some are disappearing and reappearing. They seem to still be there though, because the villagers that are visible still breed with the invisible ones. It's very annoying though because they get out of their breeding room and I don't even know they're gone. When I save and quit, and then come back sometimes they reappear. They're also sleeping where there aren't any beds. They're floating on their backs as if a bed were there. I can't screenshot because the glitch isn't actually happening right now. Please fix this I'm trying to build an iron farm.