The good news is that I think I found how to reproduce it. The sequence is something like: use Wifi (e.g. office), suspend, resume with wifi active but no network (e.g. train), suspend, resume with wifi active and known network and cable plugged-in (e.g. home) -> NM is unable to connect with the wire.
I'll try to reproduce it a couple of times, to be sure.
Guess what? It happened again :-(
The good news is that I think I found how to reproduce it. The sequence is something like: use Wifi (e.g. office), suspend, resume with wifi active but no network (e.g. train), suspend, resume with wifi active and known network and cable plugged-in (e.g. home) -> NM is unable to connect with the wire.
I'll try to reproduce it a couple of times, to be sure.