I started a Minecraft World using version 1.14. Over the course of a few hundred hours, I've expanded a naturally generated village 200 blocks long by 110 blocks wide. I started using Realms last year (2020) around version 1.16 and I began to notice that my 5 Iron Golems started disappearing as well as dozens of Villagers. I believe the issue lies around hopping in / out of nether / end portals, as when I return, my villagers are always breeding and I can visually see the number of villagers dwindle. When I take my world off of Realms (download a copy), villagers start repopulating and I can hop in and out of nether / end portals without any mobs despawning. After playing for months offline without any despawn issues, I tried Realms again after the 1.17 update and the first time I went to the nether I had a large number of missing villagers. I know the issue is not related to villagers deaths as I've had the world in Peaceful for quite some time. I also thought there might be an issue with my world, since it was created around 1.14, however I took the time to create an entirely new world on Realms with a large village like mine and the same issue happens when I use a portal. Even if I name the villagers with nametags, they still randomly despawn when I use any portal.