I am having the exact same issue. And it appeared when the pandas did.
Oh... another issue is that when I load another save that doesn't crash the game back to the dashboard, when I save and quit and exit minecraft then re-enter, my skin has been reset to Steve. Not sure if the two are related.
I have the very same problem with a world on my xbox one. The world will crash in about 10-30 seconds after loading. it is a world with a lot of redstone and repeating command blocks set for testfor @p and impulse command blocks set for teleporting.
The world worked just fine yesterday prior to me receiving a message saying that my game had been updated with a partial/demo version of the aquatic update.
Microsoft is at a loss and had me delete the local copy of the game and load the cloud copy with no prevail.
Forgot to add... this isn't a Realm only issue. I have this problem with all the worlds (online/offline) that use the Odyssey Pack.