Loading scene best practive

I apologize for the newbie question, but there is a little information available.
My app has one main scene. Originally I thought that Unity asynchronously loads the first scene in build during splash screen. Apparently it is not the case, because I can see black edges when I moving head on startup.

I think the solution would be to have another very simple scene with some loading animation and code like below:

Code (CSharp):

1. AsyncOperation async = SceneManager.LoadSceneAsync(1);
2. Application.backgroundLoadingPriority = ThreadPriority.BelowNormal;
3. while (!async.isDone)
4. {
5.   yield return null;
6. }

But that doesn't help much. I still can see edges.
How smart developers approach this problem?

 

Maybe I made a wrong word choice in the title. It actually should be:
"Game freeze when loading" or "Head tracking stops on startup"
It even present with demo scene from SDK