Netgear Nighthawk R7000 Not Connecting Through MB8600 to ISP

Hello,

I have an Nighthawk R7000, that suddenly (and I mean to the point of preventing three people from accessing their remote work) refused to connect to my Motorola MB8600 headend and in turn to connect to my ISP, Comcast. I have a backup Linksys MR7350 that I bought hastily to restore access and it works to the specifications described (few configuration options though).

In attempting to troubleshoot the Nighthawk, I rolled back the firmware to version 1.0.9.88 and updated the firmware to 1.0.11.116. I also changed the mac address settings to the device default and I reset the router. It does not see my MB8600 or the ISP line. This router/wifi router is ~3 years old and why it would fail this quickly is beyond me. Please note: We changed nothing about our configuration. This problem is an aberration.

Any help to troubleshoot would be great.

--InThisSituation