I had a villager whom I put a nametag on despawn after I loaded my world up this morning. This isn't the only time it has happened. Several times my villagers disappeared without a trace and no explanation. 

They are enclosed in safe spaces so mobs cannot get to them and they have been interacted with so it's not a matter of being a random villager.

The villagers were already located in the village and were there for several time I have played however the librarian has dissapeared. The other villager is still there and I have had no issues with it despawning.  

I thought it might be a corrupted chunk so I moved the villagers to the other side of the village after the first occurrence however that didnt seem to help.