The only other thing I can think of is to unplug all LAN Ethernet connections to the router and then only have your PC connected directly to it. Power off the router, wait 60 seconds and turn it back on. Any change? It might be worth trying this procedure twice. Once with the PC connected to the 10G port and a second time connected to a 1G port.
What's strange is that you obviously have connectivity to the router otherwise you wouldn't have been able to see the GUI and retrieve the syslog. And the router has connectivity to the internet because the syslog shows this.
EDIT: Is there any difference if you connect to the router's WiFi (as opposed to your AP's)?
Have you tried rolling back the firmware to the previous version? Some RT-AX89X users complained about their hardware freezing up after the latest firmware update.