Debugging 101: try removing all of your custom widgets. If that helps, re-add them until it fails again and you'll have your culprit. If that doesn't work then you could try the same for all the native widgets, although at that point you might also consider figuring out how to hook up dev tools to your app instead. Unfortunately that's not very easy to do in iOS, but you can find a pretty good how-to here: http://developer.telerik.com/featured/a-concise-guide-to-remote-debugging-on-ios-android-and-windows-phone/
You can update your app to the latest version. It may fix the white screen problem.