Xamarin Forms Ondisappearing() called soon after Onappearing()

Ondisappearing() called soon after Onappearing() and onappearing called right after ondisappearing..i had this issue only on one page. other pages do not have this issue.i found this when i tap on navbar back button, it does not navigate to previous page, i had to tap twice to navigate back on this particular page..then i found this problem.degraded forms version 4.0 to 3.5 and recreated new page did not solve this issue..help need...

public Cart_Page2 ()
        {
            InitializeComponent ();
        }

        protected override void OnAppearing()
        {
            base.OnAppearing();

            var vm = new Cart_page_vm();
            vm.Navigation = Navigation;
            BindingContext = vm;    
        }

        protected override void OnDisappearing()
        {
            //  MessagingCenter.Send<Cart_page>(this, "cart_page_disappear");
            //  Navigation.PopAsync();       
        }