CollectionView child added event not firing

I am using Xamarin Forms and CollectionsView.I am adding Frame child rows using SignalR. Child added event is not firing after few child is added.Is it a bug or am i doing something wrong?? I tried with CollectionView_ChildAdded event also.That one also gives this unexpected behavior.I am adding item to itemsource collection using SignalR

<CollectionView x:Name="ItemsListView"               
            ItemsSource="{Binding Items}" 
            VerticalOptions="FillAndExpand"
            SelectionMode="None"
            ItemsUpdatingScrollMode="KeepScrollOffset"  
            >
                <CollectionView.ItemTemplate>
                    <DataTemplate>
                        <Frame  x:Name="frame1" BackgroundColor="White" BorderColor="#F0F0F0" Padding="3" Margin="0,0,0,5" HasShadow="False"  CornerRadius="10" ChildAdded="frame1_ChildAdded">
                            <Grid HeightRequest="40" HorizontalOptions="FillAndExpand" VerticalOptions="Start">
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="2*"/>
                                    <ColumnDefinition Width="2*" />
                                    <ColumnDefinition Width="6*" />
                                </Grid.ColumnDefinitions>
                                <Label Grid.Column="0" x:Name="lb_TicketNumber" Text="{Binding TicketNumber}" TextColor="Black" FontSize="Large" FontAttributes="Bold" VerticalOptions="Center" Margin="20,0" HorizontalTextAlignment="Center"  />
                                <Label Grid.Column="1" Text="{Binding DeskName}" TextColor="Black" FontSize="Large" FontAttributes="Bold" VerticalOptions="Center" HorizontalTextAlignment="Center"/>
                                <Label Grid.Column="2" Text="{Binding ServiceNameEng}" TextColor="Black" FontSize="Large" FontAttributes="Bold" VerticalOptions="Center" HorizontalTextAlignment="Center" />
                            </Grid>
                        </Frame>

                    </DataTemplate>

                </CollectionView.ItemTemplate>

            </CollectionView>

below event stops firing after few times.

private void frame1_ChildAdded(object sender, ElementEventArgs e)
    {
        DisplayAlert("Child added", "OK", "OK");
    }