Have villagers in a farm, and an iron farm, and in a breeder just randomly disappear

What I expected to happen was...:
What I expected to happen was with everything lit up and proper walls in place, and villagers named they would not disappear

What actually happened 

what actually happened was they disappeared for seemingly no reason

Steps to Reproduce:
1. Put Three villagers in an iron farm
2. Put about 15 villagers at the end of a breeder in a small hut with walls and lighting
3. Put villagers in a villager ran farm, name them

4. don't know when but they will eventually just disappear