Ah, I think I had this the other day. I booted my PC, it updated, when I logged in I had no connection to the internet (ethernet). Was confused but my MBP and phone had working connections so I just rebooted. Worked fine after that.
Rebooting it helped.
I had rebooted the router for other reasons the day before and thought that could have been the reason, but seems not.
Shook my head and set it statically up rather then spend more time on DHCP I don't need. Luckily it was a desktop not a laptop. But... they have a laptop so maybe that's coming.