[Edit - this is SOLVED. I'm keeping this here for posterity, in case others have the same issue when converting older Xcode projects.]
I have an existing project that was originally created for iPad only, circa Xcode 4.
I'm currently building with Xcode 7 Beta 1. Deployment target is 8.3.
I have set the "Deployment Info" to "Universal", and have enabled Auto Layout and Size Classes.
The apps runs normally on the iPad.
Problem:
When running the app on in iPhone 6 (running 8.3), all content (including the Status Bar and any Navigation Bar) appears to occupy an area about the size of an iPhone 4, centered vertically within the screen. There are black bars on the top and bottom.
i.e. the screen is effectively letterboxed.
To test that it was not a problem with the View Controllers themselves (despite the obvious issue with the Status Bar being out of place), I dragged out a new Navigation Controller from the Object Library, and set it as the Initial View Controller. Result: same thing. (Letterboxing occurs.)
However, if I create a New Project and run it on the device, the content displays normally, occupying the entire screen. Thus the problem only occurs to my existing project.
Thanks for any suggestions.
SOLUTION
1) Add a Launch Screen:
New File -> iOS -> User Interface -> Launch Screen
2) Set the name of your new launch screen in:
[Your Project] -> General -> Launch Screen File