Workaround for https://bugzilla.xamarin.com/show_bug.cgi?id=43298

PopToRootAsync_workaround.cs

protected async Task NavigationPopToRootAsync()
{
    // Popping pages only makes sense if there are at least 2 pages on the stack.
    if (this.Navigation.NavigationStack.Count < 2)
    {
        return;
    }

    // Workaround for the issue in Xamarin.Form on Windows Phone when calling PopToRootAsync()
    // see: https://bugzilla.xamarin.com/show_bug.cgi?id=43298
    if (Device.OS == TargetPlatform.WinPhone)
    {
        // First remove the pagesfrom the stack between the root page and the current page.
        // Note: Make sure to call ToList() because removing pages will modify the NavigationStack collection.
        foreach (var page in this.Navigation.NavigationStack.Skip(1).TakeWhile(p => p != this).ToList())
        {
            this.Navigation.RemovePage(page);
        }

        // Popping the current page will load the root page again.
        await this.Navigation.PopAsync(false);
    }
    else
    {
        await this.Navigation.PopToRootAsync(false);
    }
}