I have a year and a half old Z-370 E motherboard that a few months ago stopped allowing the internet to work over Ethernet/LAN. Data can still travel over Ethernet but no internet. I have to use Wifi as my primary connection, but it's not as reliable or fast particularly during uploads, and for work that's a problem.
It's not the router as other wired devices are working fine and I've swapped Ethernet ports and cables. After narrowing it down to the PC I went through troubleshooting help with Microsoft and after checking a lot of things, they concluded I'd have to re-install Windows... drastic! And not something you want to do in the middle of a project. But I did it on a new Hard drive, a complete clean install and the internet still didn't work over Ethernet. So I'm left to assume it's a motherboard issue. Have you heard of this happening? Could it be a setting in the BIOS?