Steps to reproduce:
1. Create a new empty project with a blank scene.
2. Switch platform to UWP and enable windows MR support in Player settings
3. Build the project and open in VS
4. Create App in VS (Project > Store > Create App packages).
5. Install the package.
6. Launch MR Portal. Place the app in the Cliff house and select it to launch the app.
7. Right after selecting the app to launch, keep holding the trigger button of the MR controller.

Expected results: Project launches in without hanging at the loading screen.
Actual results: After the loading transition, you will become locked in a black screen. You need to press the trigger again to exit this screen.

Reproduced with: 2018.2.0b4, 2018.1.0f2, 2017.4.3f1, 2017.3.2f1, 2017.2.3f1