I would guess that an exception is being thrown somewhere. I'm not sure if there's a good way to see console output from an OpenFL app running on iOS, though. On Android, if you can just run
openfl test android -debug on your computer, and it will automatically install and launch the app, and you'll see the
trace() output and exception stacks in your computer's terminal. However, since you need to install through Xcode to put an app on iOS devices, I'm not sure how to see all that same stuff in real-time on your computer while running the app on iOS.
I know that there's an HXCPP debugger, but I'm not sure if that works only for apps on your local computer, or if there's a supported way to hook it up to apps running on mobile devices too.
For the record, I can say that I always run the Feathers UI components-explorer sample on iOS before every release. I navigate to every screen in the app to check that all components are working correctly.