I have found a fix for this issue and it seems to currently be working. What I have done is found out accidentally is that when you load a world and wait until after the bar disappears, press the home button once(on ios) and the just open the app again. What you should see now is the game loading like it is when you first open it and then it should bring you straight into your world. You can try this to see if it works but I have tested it many times with different scenarios to see if it kept working and it did.
This has happens to me as well and I tried re-downloading my game but lost all my worlds. BUT I found a fix. You just have to sign out and then sign back in and it should be okay. Hope this helped!
I have found a fix for this issue and it seems to currently be working. What I have done is found out accidentally is that when you load a world and wait until after the bar disappears, press the home button once(on ios) and the just open the app again. What you should see now is the game loading like it is when you first open it and then it should bring you straight into your world. You can try this to see if it works but I have tested it many times with different scenarios to see if it kept working and it did.