Villager AI buggy

One day I stole an NPC villager's house and made a chicken farm in the backyard. I used iron doors so that they could not come in. At night ALL the villagers stay just outside my house, and I kept hearing villagers' dying sound BUT they refused to run away from the zombies and stay at their house. The seed is 5550216516149607793. I forgot to take a screenshot because I went out to deal with the zombies (survival no cheats)

1. Go to the house which has a backyard
2. Replace the door with an iron one
3. spawn chickens/ lead chickens to the backyard
4. customize the house/ backyard/ whatever
5. Wait till night
6. the villagers crowed around outside
7. Go outside and spawn 100 zombies
8. they refuse to move