iOS Development Black Screen (No Error)

Releasing my first app on iOS, works perfectly on Android, transferred the project to a Mac Mini, where I built it and ran it in XCode.

When the game launches it shows the Game Object in the scene (A single sphere in the centre), with a black background, before loading in all of the UI elements behind it. This happens on both iPod Touch and iPhone.

However, when I submit it to ITunes Connect it is rejected with the statement:

We discovered one or more bugs in your app when reviewed on iPad running iOS 11.4.1 on Wi-Fi connected to an IPv6 network.

Your app continues to launch to a blank black screen without functionality.

This error had previously occurred on iPhone, however this was solved by changing the Camera Clear Flags to "Depth only", as it was "Don't Clear" before.

I have been trying to solve this problem for three days straight, any sort of advice would be appreciated.

Thank You