Thanks for posying your concern here!Can you please answer/try the following:
Have you been able to log into the app before?
Is your phone up-to-date?
Have you tried re-downloading the app?
Hi, I have the same issue. I have an iPhone 5 and downloaded it from the app store. Everything is up to date. I have tried unlinking and relinking my Gamertag. I also tried removing and re-downloading the app. Every attempt is the same, app loads starts to login after I enter my info then all I see is the ghosts background. App has never crashed.