After the most recent aquatic update on Xbox One, I play the Windows 10 Edition on Xbox One, all 3 copies of my Survival world that is like 7 or 8 years old are mis-titled and greyed out. When selected in the options the seed is 0 or -1 and there are no options. If you try to load it the game crashes. What happened, years of work is gone or inaccessible now.

 
The world is but the name is all jibberish on two saves of it and the backup save i have the name is correct but all three the image is greyed out on the save itself.
 
When you try to load any of the 3 saves of it the whole game crashes.
 
If you go into the settings tab of each copy there is no game type listed, no name listed, and the seed is 0 or like -1 or something insensible.
 
There are other worlds like my daughters creative world and my girlfriends world that weren't affected though.
 
I am going to go through some old stream footage to find my world's actual seed, dunno if will help but I will have it shortly if needed.