After minimising Minecraft and not going back into the game for several (usually 10 or more) minutes, the game will not allow the player to join any servers (including Realms, featured servers and servers added by the player) and will display the message "Unable to connect to world" every time. The only solution to this problem currently is to restart the game.
Steps to reproduce: launch minecraft on iOS, minimise the game windows, use other apps in meantime and wait several (usually 10 or more) minutes and open minecraft again. The game now will not allow the player to join any external servers, displaying the "Unable to connect to world" error
Expected behavior: the game allows players to join any servers/realms after having been minimised for a long period of time.