I had created a copy of the realm world to get some nice atmospheric shots for myself. I changed my game mode to creative in the copy, and took the pictures. I hop back onto the realm, to find it's been switched to creative, somehow.

So like I said the realm is now in creative. It's not a big deal, but this was the first time my friends and I had gotten some of the 1.16 achievements, and we had worked very hard on the world. Again I did not change the realm, the UI for the realm is different than the one for solo worlds, and I would have noticed. Another reason I knew this was a glitch was because when I was in the copy I had unequipped my armour and left my house, while in the actual realm I was still inside with my armour equipped.