I've been noticing over the course of two weeks that my villagers randomly disappear on a realm. I've also noticed that when a villager is sleeping they will drift/ fly in a straight line in any direction. I've tried filling in any caves nearby and monitoring them but they still disappear. Additonally, I often have to relog into the realm for the villagers to reappear and tried relogging again today but to no avail. Please help me out, thank you. 

Side note: I keep my villagers in a base underground to avoid having them run away, this is a screenshot of a random villager I found