Just reading up on Thunderbolt + the Ethernet adapter, and one buyer's review says he had to turn off his Air's wifi.
On Windows myself I found on some machines that were on wireless, just plugging in an Ethernet cable didn't automatically replace the existing wifi connection.
Probably a red herring but worth a try.
The indispensable man or woman passes from the scene, and what happens next is more or less the same thing as was happening before.
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