Try disabling Ethernet power saving in your bios - it's related to the issue, the issue is that the Ethernet port is going to sleep when it shouldn't be and then sometimes also not waking up. It's a hardware flaw so Intel can't easily fix it, the hardware flaw makes the Ethernet port incompatible with the standardised Ethernet power saving standards
You could also switch to wifi or buy an PCIE Ethernet network card. Either will fix the issue as well
That's disappointing. I'm in the process of preparing the parts I want for my new build and that's the board I was planning to go for. I use Ethernet to connect as we have Ethernet ports in all the rooms with our house being a new build with FTTP. Is this issue specific to this motherboard or is there a wider issue with X670 boards?