Hello,
There appears to be an issue with how realms handle simulation distances.
Whenever I upload a world to the realm(with a simulation distance of 12) It appears to be reset to its original distance.

Steps to reproduce:
1. create a world and set its simulation distance to 12.
2. upload said world to realm.
3. join the world. If you run

/fill ~90 ~ ~90 ~-90 ~ ~-90 dirt

you will find that it does not work. This command only works when the simulation distance is 12.

I do hope this issue is resolved in future updates. As this has the serious potential to break many marketplace maps.