Add and Delete Tabbed page children when running an app

Good day,

Have this problem accrued after updating to Forms 1.3.1 - before the code was working fine (it is also working on Android).
I have settings window where in changing data in the picker I initiate an event:

public void tabSettings_PropertyChanged(Object sender, PropertyChangedEventArgs e)
{

        this.Children.Clear();

        if (e.PropertyName == "settingsSelectedConference")
        {
            try
            {
                   this.Children.Add(new projectsT() { Title = "Projects" });
            }
            catch (Exception ex)
            {
                DependencyService.Get<IReadFiles>().addRecord("Error updating screen" + ex.Message);
            }

after running this code App is crushing with System.NullReferenceException: Object reference not set to an instance of an object.

As I said - on android it works fine.... but crushes on iOS

Any thoughts? Thank you