Mason Villagers despawning

I am unsure what is going on wth my realm, but I have had 3 Mason villagers despawn or disappear on me. I had 2 trapped in a house where the minimum light level was 8 (so I don't believe monsters can spawn) and another one in a protected village.

At first I thought the one from the protected village was a runaway, but I know that the other mason villagers were locked into a place with job blocks and beds and light level of 8 or higher. Can you tell me if this is a bug?