so i was playing on a friends realm, and i traveled 5-6k blocks to and from a mushroom island to get mooshrooms, i got back to my base and went to get wheat to lead them to a pen, and when i got back to them they despawned, my guess is the realms simulation distance, or whatever setting mobs use to despawn, ive noticed this has happened with another mob, the pillager, also despawning when you move too far away from the boat