PRISM / NavigateAsync not working within await

I am using Dapper to connect to a SQL-Server. When I start my App I want to make sure that there is a connection before I open my Page.
Everything works perfectly except the Page is not showing or is kind of "Empty".
The result ==result.Success, no errors are shown and all steps are executed in the ViewModel of my Page. And there are also no errors in the Constructor of the "CodeBehind" (InitializeComponent();)

Without the (if(await...) the Page is opening.

if (await DapperEngine.CheckConnection(Prefs.ConnectionString) == true)
{
    result = await NavigationService.NavigateAsync("NavigationPage/MainView");
    if (result.Success == false)
    {

    }
}

Any Ideas ?