The original bug was on Windows Phone 10, but it can be reproduced with Windows Standalone.

Whenever app is launched on Windows Phone 10, plane texture becomes transparent.

Tested on 5.3.2p4, 5.4.0b7.
On 5.2 versions getting black screen.

Repro screenshots:

Editor gameview:
https://oc.unity3d.com/index.php/s/nlNGWozRMUUq5Fc

Windows Phone 10 & Windows Standalone:
https://oc.unity3d.com/index.php/s/4AFurrnnGlfGKH6

Repro steps:
1. Build to Windows Standalone, ensure graphics API is DX11
2. Run the executable with -force-feature-level-9.3 (This what Windows Phone 10 is using)
3. See the transparent plane, which is actually skybox reflected.

Workaround: Untick Reflections in background2 material inspector

I am not sure if this is a bug or by design, you decide.