Your device may be holding onto some "bad data". The best way to clear any of this "bad data" would be deleting and reinstalling the app on your device.

Don't worry about losing your progress - your account information is stored on our servers, not remotely on your device.

When you reopen the game, you will automatically be logged in via the Guest method. If this isn't your existing progress, simply tap Logout from the Options menu, and then select your login method from the main menu.