Navigation in OnAppearing() method works wrong

Question

I got 2 pages FirstPage which is Content and SecondPage which is Tabbed page FirstPage contains OnAppearing method

protected override void OnAppearing()
    {
        if (Preferences.Get("IsLogged", false) == true && App.BugFix == true)
        {
            Task.Run(async () =>
            {
                await Navigation.PushModalAsync(new MainTabPage());
            });
        }
    }

When the conditions is true it navigated to the TabPage ( for example it has 3 children pages), but i can see first children(page) and there is no ToolBar image how it should look

I changed this part of code

Task.Run(async () =>
            {
                await Navigation.PushModalAsync(new MainTabPage());
            });

to

Dispatcher.Dispatch(async () =>
            {
                await Navigation.PushModalAsync(new MainTabPage());
            });

and now it works as expected, but it has visual problem, before it navigates to the tab page it shows the FirstPage for like a second.