I have been playing for weeks in my husband's world. This evening we updated to the second aquatic update and were playing together, successfully. I logged out to do something else (was in the nether, if it matters). Later when I logged back in, I was at the origin and had no things in my inventory (including the armor I had been wearing) or in my Ender chest. 

My inventory had included an Ender chest with four shulker boxes and another Ender chest inside of it (containing everything of value I've found/created in the game so far). 

The things I was doing prior to logging out/logging back in were there (I had put a map on a wall and had put some items away in chests - those things are still there in my husband's world.) But all my inventory is now gone. 

Actually, one other thing happened - I wasn't logged in to Xbox Live, but I was able to log in to my husband's world anyway (? this makes no sense, right?) and was at the origin. The timeline is something like this:

• Husband comes home from work and updates to latest Windows Store version.
• Husband plays.
• I join and play. I put a map on the wall and slime balls in a chest.
• I log out to go do laundry.
• I go to log back in after laundry, but somehow I'm not logged in to Xbox Live. I get logged in as Steve and I'm at the origin with no things. I log out and go make sure I'm logged in to Xbox Live.
• I log back in as me (SevralTimez) and I have my stuff.
• I go to the Nether.
• We decide to watch TV IRL, so I log out still in the Nether. My husband logs out too.
• TV is boring, so my husband and I go back to play Minecraft.
• Now when I log in, I have no things and I'm at the origin, but I'm logged in as me, SevralTimez.
• I log out again and back in again to see if my stuff can magically re-appear, but that doesn't happen.
• Now I'm sad, but I can re-make my things, and I hope this doesn't happen to anyone else!