Minecraft bedrocks world storage is based on a small amount of storage which is stored within the game itself. I'm fairly certain that the size of the realm world is bigger than the storage in game which is causing the realm bug on console. I'm not familiar with how coding or anything like that works but in theory this sounds like the problem. I don't know if it would be possible to change the storage from in game to running off of the system storage or an external storage device.