This is a bug that just recently started happening to me, maybe two weeks before the Nether Update dropped and it still happens to me. When trying to start the game only using my Cellular Data, the game will do one of two things. It’ll either a) crash before getting to the main menu or b) get to the home menu, but it will be unbearably slow (about 2 frames per 6 seconds). If you attempt to navigate your way to your worlds, you’ll find that the worlds will load normally and they’ll play normally at normal speeds. It’s only the main menu that slows down this much. I even tried deleting the app itself and resetting my phone to no avail. Starting the application on WiFi however completely eradicates this problem.