Around 7:15 PM this evening Debian networking went away.

     I logged into the console and everything at first appeared normal but I could not ping or connect to anything outside.

     I tried restarting networking, it was uneventful but did not restore connectivity.  I think restarted NetworkManager but it failed to start with the error stating it had been restarted too frequently.

     At this point I rebooted the machine.  After it came back up there was still no networking but the NetworkManager was working again.  I went in and found the Ethernet device was just gone.  I recreated it and now everything is working again.

     This must be a new NetPlan feature.