Put the summary of the bug you're having here

What I expected to happen was...:
Farmer villager not disappearing, when there are blocks all around him.

What actually happened was...:
He disappears once in two days. (Third time now)

Steps to Reproduce:
I have built this farm:

https://www.youtube.com/watch?v=q0bq-RnttBU

Second level farmer keeps disappearing.