iOS iPhone app not displaying correctly on some devices

So I've been working on a PDF reader for iOS, the app itself works fine on iPhone 6 and I think 5 as well, however on iPhone 4S and when running in compatibility mode on iPad it only displays this:

iOS app on iPad /iPhone 4S

I cannot submit my app to the iTunes store without fixing this issue, does anybody know what is causing it?

The app is coded in Objective C