Well, one of the Nuc is connected directly to the router, the other is connected by a switch. They are in different buildings, separated a few meters from each other, with different electrical installation. The network has a total of 10 machines of different types connected by cable and only the two Nuc have failed. I'm also surprised that they fail at the same time. Regards
After disconnecting the power and reconnecting after a few seconds, the adapter works again. The connector Leds work again and the adapter appears again. In one of the Nuc that lost the network configuration and after reconfiguring the two return to work.
I have no idea why the adapter could be frozen in this way.
Thanks to user Al Hill for his interest.
thanks for the idea of the "ground loop".
I have been inquiring into the history of the installation of the two buildings, I am relatively new here, and it seems that this is full of failures of this type
The UPS network card has also been frozen more than once having to remove the power to make it work again. The alarm system, also connected to the router, has also given failures. Even the office lights go off without any justification!
In the words of my boss, "we are chasing a ghost for a long time".
Everything points to a ground loop or an electrical derivation.
Thanks again and regards.