I have a XAML app that starts as a XAML app and then on some page it opens a new view (using the ApplicationViewSwitcher.TryShowAsStandaloneAsync) where it initializes Unity and enters the Holographic View. This is working fine on HoloLens, but it does not work in the Mixed Reality Portal. As long as I initialize Unity in the new view that is not the main application view, Unity enters paused mode - nothing is being rendered except for a couple of frames at the beginning (sometimes not even that and the screen just stays blank). I am using Unity 2017.2.0f3-MRTP3, because with the 2017.2.0f3 release as well as 2017.3 beta the XAML app does not work at all - it is always frozen. With the Unity 2017.2.0f3-MRTP3 it works fine when I initialize Unity in the main view, but unfortunately I cannot do that because I also need the XAML view.
This should be fixed in the latest MRTP build: [Custom Build] 2017.2 RC MRTP (Windows Mixed Reality Technical Preview)
I am using the latest MRTP3 build. I can confirm this issue has been fixed when Unity is initialized in the main view (something which was not working in other versions of Unity), but the issue is still there when it is being initialized from the secondary view. Unless there is some newer build (MRTP4?), then the issue is still reproducible.
Can you submit a bug report with a repro project? We’ll take a look.