The symptoms described above most often indicate that the Ethernet port device is being detected, however macOS is not automatically creating a new network service for the device. In most cases manually adding the service by following this procedure can help:

1. Click on ‘System Preferences’ (gear icon in the macOS 'Dock').
2. Click on the ‘Network’ Application (globe icon).
3. In the bottom left-hand corner of the ‘Network’ application, click on the “+” (plus) sign to add a new service.
4. Click on the ‘Interface’ drop down and select ‘Thunderbolt Ethernet Slot 1’.
5. Leave the ‘Service Name’ populated with the default name and then click the ‘Create’ button.
6. Click the ‘Apply’ button in the lower right-hand corner of the application to apply the changes.
7. Wait a few moments to see if the Ethernet adapter in the dock starts working.