Villagers are disappearing out of iron farm for no reason

My friends and I have been playing on a realm for some time, I needed a lot of hoppers so to supply me with iron I built an iron farm. Unfortunately The villagers in the farm keep disappearing for no good reason, they're up in the sky so no mobs can reach them, the whole cage is lit up and spawn proof, and the weather cycle is off so they aren't being struck by lightning. We've replaced these villagers quite a few times as well. From what i can gather this happens once I unload the chunks by going to the nether or leaving the area. I've tried renaming them, trading with them, and both at the same time. They stick around as long as i'm in the area however loading the farm even throughout the night which is how i know mobs can't reach them. If there is a solution that i haven't found please let me know because I'm clueless as to why this is happening. Please look into it a little more because from what i can see this sort of thing has been an issue for a little while