I want to start this off by saying I searched for this issue before, and only found posts listed 1-2 years ago. I'm sorry if this has been mentioned recently but I couldn't find posts regarding it.

I started a world on my Switch with my girlfriend a few months ago, and ever since we've managed to create the biggest survival world I've ever played on. We played on split screen the whole time, but the more we built, the more lagging and freezing we encountered. One day I decided to transfer the world to a realm, so I could play on Windows 10 (with RTX) and she could play on Switch. It was working perfectly fine for quite a while, but recently we've encountered a major issue with despawning, and it seems to be completely random. We've had two named zombies sitting in a pit that have been alive since the start of the world, yet we have some animals that we capture and then they despawn later. They're all named, and they're all sitting in enclosed areas. I have an automatic wool farm and today, I logged on, and my minecart with hopper despawned, along with finding 2 sheep dead, although the sheep are completely safe in the farm and have been there since nearly the start of the world. I also had an issue where the minecart with hopper in my automatic sugar cane farm despawned. Other than that, my girlfriend tamed a dog about a week ago, made it sit, and came back later and it had despawned. I also have a small enclosure for fish to swim around, and I have one salmon and one cod kept in there, although the cod despawned with no possible way of having died. The pictures below are for reference of how big our town is (if the size matters for despawning).

About the weather issues I mentioned, my girlfriend logged in right before I decided to fill out the bug report, and while it was raining on her screen, the weather was clear on my screen. I have 2 pictures where we're staring at eachother while standing on our current projects and you can see the difference. Other than that, I have had a day before (playing by myself on the same world) where it was raining, but Endermen weren't being injured by it, and zombies lit on fire stayed on fire.

This is getting really frustrating and I don't understand it, because everyone says named mobs can't despawn, and it's more annoying when pieces of my redstone builds are despawning.

I included a picture (with RTX turned off) of my sheep farm to show what it looks like. This is my second time making this specific design for this farm, and this is my very first time encountering an issue where the minecart despawns and sheep die.