luetm

public ObservableCollection Positions  // << dependency property
{ 
  get { /* ... */ }
  set { /* ... */ }
}

private volatile int _queue;
private readonly object _queueLock = new object();

private async void OnItemsSourceChanged(object sender, NotifyCollectionChangedEventArgs e)

luetm

public ObservableCollection<IInvoicePosition> Positions  // << dependency property
{ 
  get { /* ... */ }
  set { /* ... */ }
}

private volatile int _queue;
private readonly object _queueLock = new object();

private async void OnItemsSourceChanged(object sender, NotifyCollectionChangedEventArgs e)