ListView (inside Grid) won't rescale after (async) loading Items

All works fine when loading the ListView with content inside the constructor of the page.

But when loaded async after the page is fully loaded, the ListView stays small in height.

Any suggestions how to redraw/invalidatemeasures for the ListView?

A part of the layout:

  <Grid HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand" BackgroundColor="Gray" >      
                <Grid.ColumnDefinitions>
            <ColumnDefinition Width="Auto" />
                        <ColumnDefinition Width="*" />
              </Grid.ColumnDefinitions> 
        <ListView x:Name="GlossaryListView" Grid.ColumnSpan="2" ItemsSource="{Binding GlossaryItems}" 
                  VerticalOptions="FillAndExpand" BackgroundColor="Red"
                  HorizontalOptions="FillAndExpand" HasUnevenRows="true" >
            <ListView.ItemTemplate>
            <DataTemplate>
              <ViewCell>
.....