Igloo's Pre-spawned Mobs Don't Exist for a Time

I have encountered 2 igloos where the villager and the zombie have not existed yet they could be heard. They could not be interacted with in any way. After waiting about 2 minutes, they would then appear.

Seed: 7421865649510581170
Location One: -16850 39 15100
Location Two: -16107 50 15725