OnResume/OnSleep do not fire on UWP

I have a cross-plat app that i have created (load a webview by passing lat/long)
I would like to refresh my app by sending latest position each time the user resumes the app.
The code below works fine on iPad, but on my lumia 950 the onresume/onsleep never fires when i hit back button or hit home button on my phone.
The only time the onsleep fires is when i hold the back button and terminate the app using the X

Also is there a better way to refresh the webview by passing new position then doing it onresume?

public class App : Application
{
    public App()
    {


        var navPage = new NavigationPage(new WebPage());

        MainPage = navPage;
    }


    protected override void OnStart()
    {

        NavigationPage.SetHasNavigationBar(this, false);

        Debug.WriteLine("Started");

    }

    protected override void OnSleep()
    {
        Debug.WriteLine("Slept");

    }

    protected override void OnResume()
    {
        Debug.WriteLine("Resumed");
        var navPage = new NavigationPage(new WebPage());

        MainPage = navPage;

    }

}