I see you set
Application.runInBackground = true;
Inside PlayFabHttp.cs
That thing messes anyone's code that relies on application going in/out of background. Of course, I can comment out that line, but then it affects PlayFab's background activity...
I think it's better if you adjust all your coroutines to use unscaled time, so everything works in background for PlayFab, but leaves to developers the chosen application behavior...