This excellent fix has been found and all credit goes to MartynMacMan!

This is for macs which show the thunderbolt interface in the System Report but wont add via the Network Connections Control Panel.

  1. Unplug thunderbolt adaptor
  2. Reboot
  3. Login as root
  4. Remove all interfaces from all locations you have in Network Connections control panel.
  5. Apply settings to all locations.
  6. Add a Thunderbolt Bridge
  7. Apply
  8. Remove Thunderbolt bridge
  9. Apply
  10. Now add the Thunderbolt Ethernet
  11. Apply
  12. Should now show in the list!
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