When Uploading World to Realm, Blocks below X and Z: 0 Get reset

BEFORE YOU READ: I AM AWARE THIS IS A DUPLICATE. I AM JUST PUTTING MORE DETAIL INTO MY PROBLEM. Now to the description!

So I tried to upgrade my old server by buying a realm. But when I put the old world on, I noticed that a lot of my world has been reset! I tried to get as much info as possible. One of my observations is that this was only happening below the X coordinate of 0. In case this has something do do with the problem, the world was originally created in 1.8, and has lived through 1.8, 1.9, and now 1.10. I have attached some photos of the world and a crash report that while you probably don't need, but I put in anyway.

EDIT: I have now just discovered that blocks below Z coordinate 0 were reset too... This is all very strange...