WPF ItemContainerGenerator.Status is NotStarted

Question

I have a datagrid, which I scroll to top or there arent enough records to be there a scroll, then ItemContainerGenerator.Status is NotStarted. Why is that? How force ItemContainerGenerator.Status to change status to be ready? Only when I scroll, then ItemContainerGenerator changes a status.

private void ItemContainerGenerator_StatusChanged(object sender, EventArgs e) {
    if ((sender as ItemContainerGenerator).Status == GeneratorStatus.ContainerGenerated) {
        
        if (obj != null) {
            Win.Dispatcher.BeginInvoke(new Action(() => {
                Win.SelectedItem = obj;
                Win.ScrollIntoView(obj);
            }), DispatcherPriority.Render);
        }
    }

Edit: User can open a few datagrid window. There is a code, which opens DataGrid Window. The bug might be related to ShowAsync

protected override async Task ExecuteAsync(OleMenuCmdEventArgs e) 
{
   var record = GetRecord(); //I get a record from listbox to select in Datagrid
   ToolWindowPane win = Package.FindToolWindow(typeOf(Pane), key, false);

   if (win!= null) {
     MyToolWindow.MyDictionary[record.Name].SelectRecord(record.Name);
     return MyToolWindow.ShowAsync(key, false);
   }
  ///... other code, which open window for the first time etc.
}

The window class:

public MyToolWindow() //constructor
{
  SelectRecord(record);
}

private void SelectRecord(string record) 
{  var obj = LookForRecordToSelect(record);
   datagrid.SelectedItem = obj;
   datagrid.ScrollIntoView(obj);
}

It might first selection works, because it's defined in constructor