Apple TV 4K (3rd generation) fails to connect to the internet via ethernet

I’m having issues with Apple TV 4K (3rd generation) connecting to the internet via ethernet. This is the first time we have tried connecting it to ethernet (we had the CAT6 cable run to our living room today). It works fine on wifi. The Apple TV shows as connected in Network settings, with an IP, ethernet address, etc, but all apps report ‘No internet connection’. I have tried restarting the Apple TV, power cycling it and resetting it as well as power cycling the modem. I can rule out a faulty ethernet cable as it works fine connected to multiple other devices.

After being on the phone with Apple Support for 35 minutes, their suggestion was to take it to an authorized service centre to diagnose the ethernet port, of which we don’t have anything near where we live.

Does anyone have any other suggestions of what to try?