The world that is affected is just a regular world, not a realms. I was in the end and i had just travelled back to the main island where the portal to the overworld is, however upon arrival a lot of the chunks hadn't loaded in. I thought it was just a minor glitch so i saved and left and now when i try to log back in, the building terrain bar is stuck at the very end.

(Some additional information)

The world was created under my brothers account, so when I couldn't log in, he travelled to the end and was able to see my character, (whilst i was still stuck on the loading screen). We thought that killing me would send me back to the overworld, however i couldn't die and was just standing there. The chunks on his screen were loaded, so I thought that the glitch had been resolved so he saved and left, in an attempt for me to be able to try and log in again. Sadly, once he saved and left, the same thing happened for him so now it seems as though we are officially locked out of that world.