I’ve explored a mansion 14000 blocks away from spawn a while ago and a chunk of it at the corner is missing. I’ve seen this happen in other people’s worlds as well and it does not affect every mansion. For instance, the second mansion I explored, 21000 blocks away from spawn, does not have the same issue. However there’s little chance I’ll be able to travel to either of these mansions to take screenshots in the near future due to their remote location from my spawn base. In addition, I’ve made a duplicate of my world and the problem did not exist again. That means the missing corner of the mansion is not exclusive to the seed of the word I’m playing on.