As an iOS developer, I think most developers facing the issue of getting your iOS devices messed up during the development. At one time, I couldn’t leave Game Center Sandbox mode. Then I found the ways to solve it.
- Open Game Center and login your sandbox account. If you don’t have one, then create one!
- After login, now you need to Sign Out.
- Close Game Center and ensure it not in the multitasking bar.
- Open Game Center and now you should back to your normal mode.
I guess some cookies issue causing the Game Center thinking developers want to use the Sandbox mode, until you finally sign out and remove it.