Villagers disappearing

I’ve been playing on a realm with 2 friends for months now, and I’ve had the same issue repeatedly. I have 8 villagers who are fully safe and locked up in an area, but they keep disappearing. The ones that they are in have around 12 more, but every so often, when I go to check in on them, those same 8 will fully disappear. There’s no way for a zombie to spawn in the area as it’s fully lit, there’s a bell nearby, I named them, they also have their bed and job blocks. But no matter what I do, they keep disappearing. I need this fixed because it’s getting increasingly frustrating to even play, as we either have to load an old backup or I have to heal a whole bunch of zombie villagers all over again. This genuinely is sucking the fun out of playing so please help.