So i have made a villager "quarantine" zone in my home area and the are multiple villagers in here trapped. However everytime i return back to the area with all villagers, some of them would disappear and i would need to breed news one but this only recently happen and as at the start when we first had villagers, this problem never occurred.

I'm not sure what is the cause of it and i haven't seen any other reports on this problem, i could suspect something about the reload of the chunk and how that the file of the villagers don't permanently save or due to the update of Minecraft or switching to a realm.