This is usually not a change at all. A carrier can confirm the deep-sea leg and not
yet publish the onward feeder leg, so there is no vessel to show for it. See
no tracking data.
Example
A carrier has confirmed the deep-sea leg for a shipment, but the onward feeder leg has not yet been published. Because that feeder leg is still missing, there is no vessel to show for it. This is usually not a change at all; it is a different problem from tracking data being unavailable.