I'm having the same issue. My game world I created, loads but nothing can be interacted with. I can open a chest but it wont close. I can climb up scaffolding, but can't get down a gain. Then after about 30 seconds or so the game closes and then i get a "disconnected from Server" message. After multiple tries to relog in, it happens again. And in some instances now, the entire ground has disappeared before it crashes with the same server error message.
I reloaded a previous save and everything worked, until I went near a portal. The game became unresponsive and destroying a block from the portal, didn't actually turn off the portal. It was still active. Once I moved away from the portal, most of the worlds textures disappeared and took approx 2-3 mins to reload in. Going back to the portal resulted in the same issue, but this time I couldn't even remove any blocks. And when moving away again, textures missing. Closing down the session and reloading, then resulted in a server connection and the save file going from 70MB to almost 190-200MB.
I then tried to download a previous save and put it in the non-realm saves section and the file ballooned out to a massive 1.9GB and wont even open. So, it appears that whatever is affecting the realms save transfers over to a normal save, making the game unplayable.
So, you may want to look at portals as having something to do, with this issue.