What OS are you currently running (including version #) 7.1.1
Did you delete the game and reinstall it, or just update over the old build? Update, probably.
If you updated, did you manually update it, or allow the store to auto-update it? Auto-update.
This issue started this morning. No issue previously. I start the game, click "Enter Vault XXX" and then it begins to load, about 10 seconds later it hangs and will not get past that screen. I've waited several minutes a few times. If I go back to home screen, and open it again, I can sort of see my vault, but nothing happens. Exiting the app and restarting does not help. Closing all other apps does not help. Restarting my phone does not help. I'd like to keep playing now that I have a large vault and spent money. I have about 125 dwellers, maybe 15 in the wasteland.