Despawning Issues

Our realm has had named mobs, including an Elder Guardian despawn for no apparent reason for around three weeks. It started with villagers despawning while being in a contained unit consistently. We had lost between 5-10 Villagers after the 1.16 update, and we have noticed the same problem with sheep as well. Some of these sheep have been named which has caused some problems as they were our only source of brown wool. Lastly, we just found out our Elder Guardian that we had captured has disappeared, and we are extremely disappointed, because we spent a lot of time moving him to our town, and we are scared to bring another one over in fear of it despawning as well. We really enjoy playing Minecraft and doing crazy, over-the-top things, but it's getting really frustrating to replace mobs that have been named/shouldn't despawn. We would really appreciate it if you could explain why our mobs are disappearing/fix this bug. We would like to move more Elder Guardians at some point, but until we know they won't disappear, we are forced to put that project on hold. Thank you for your time, and we hope to confidently play your game again soon.