Entities such as my horses and villagers keep disappearing even though they’re name tagged they just vanish they are all kept in a room but they vanish!

So I have had 3 villagers in an area for a long time and one of them was a mending villager that took forever to obtain and when I got onto my world they were just gone, it happened before but with a lot of horses and donkeys I had.

i would appreciate it if this bug could be fixed as soon as possible.

Thanks