I will see that message every now and then and yesterday, during that testing session, it happened. Rebooting the Modem seemed to fix that.
Are there any special settings with Xfinity being your ISP? Are you needing to clone a MAC address or anything like that?
I will be looking for situation regarding Xfinity to see if anything pops up. I have already found a thread regarding using a Static IP address and MAC cloning. I will assume you have your Gateway in bypass mode.
Some good news and some bad news...
Good news is the DHCP issue was absolutely on the ISP end and everything worked the next morning. Bad news is I'm still seeing WAN data transfer speeds being inconsistent over Ethernet, something I don't see when I use a different router as my primary. Starting to think it's just how this model is and I'm ready to give up on it.
After a month of testing the crap out of multiple GT-AXE16000 units, I'm a bit burnt out and ready to just move on with the "lesser" device that doesn't have these issues. You've all been wonderfully helpful and hopefully it's just my bad luck or something incompatible on my end between my hardware and this specific router.
I read elsewhere that the AXE16000 has trouble transferring data from WAN to LAN on the 10Gbs ports when the traffic analyser features are turned on. I have a 3Gbs Internet service and was having issues with the speed test on my MacBook Pro being around 400-500Mbs slower than the speed test on the router which was receiving the full speed. Turning off all the traffic analyser features 'fixed' the problem for me.