Comment # 4 on bug 1171677 from Ivan Murray-Smith

I've since established it doesn't seem to be a networking issue as such but
rather a problem with the USB system, the ethernet card is built into a little
external box that connects via USB C.

Normally you could reset things by just unplugging it and plugging it in again,
however when the network goes does this happens:

The eth lights stay on
The mouse, plugged into the same external box, keeps working fine

However if I unplug the USB C connector and reconnect it, everything connected
via the external box is dead.