Northbound notification events not captured

I am trying to capture location update notifications with the Python Sample Notification Listener (sample code).  The python listener which is running on my computer does not see any notifications even though it is registered with the MSE (manage -> notifications).  "Waiting for connection" message is displayed.  Wireshark captures show packets coming in however not being acknowledged.  What could be the issue?

You must set port forwarding to forward Internet applications to a LAN device. 
For example, the notification subscription is set to your public IP Address using port 4321.
In your residential gateway routers firewall, set the ports or port ranges required to forward notifications to your private IP Address.