What I expected to happen was...:
I should be able to play on my Minecraft Realm I payed for.

What actually happened was...:
I played on my Realm once. I changed the world. Then I could no longer join the Realm or change the world. This happened to my friends Realm also.

Steps to Reproduce:

1. Create a world with the Caves & Cliffs Experimental Features on a singleplayer world.
2. Upload that world to your Realm
3. Unable to play on or edit Realm (You should be stuck at an endless load screen when trying to upload a new world.)