I named several villagers and a few iron golems in a village near me and they randomly disappeared. The villagers had claimed beds and workstations before despawning. When I returned and found them missing, baby villagers had replaced them already and had claimed their beds. This happened after I left the village (and the chunk was no longer loaded) and then returned some time later. I never left the overworld. This also occurred to a named polar bear that was in a different part of my world. The bear was attached to a lead and when I returned the lead was still knitted around the post but the bear was gone. Breaking the lead did not drop the lead as it should have either.