Perhaps context has been lost, and the textures are not restored correctly. You can test context loss in the AIR simulator on desktop by manually calling Starling.context.dispose(). If you can get the same thing to happen on desktop, it will be easier to debug.
For complete details, see Starling Manual: Context Loss.
If context seems to restore correctly on desktop, then there may be a runtime error that is being thrown only on your mobile device. To check for that, I recommend connecting the debugger to your app while it's running on your device. The debugger should pause if there's a runtime error and give you some clues.