Panoramic Modem and Asus Router losing connection

I've had this problem with previous modems and router models, but since I recently upgraded to the CGM4981 COX modem and the ASUS RT-BE88U this problem happens a lot.

I see the speed drop from ~2gb to ~30mb, so I reboot the router - no change, so I reset the modem - no fix, but now I have no connection between the modem and the router (router red light turns on).

I got it to work again the other day by leaving everything off for a day, reset everything to factor defaults, and eventually things got happy again. Its not practical to reset the router to factory defaults continually as I have 4 aimesh nodes around the house that then need to be reconfigured.

Is there something being cached somewhere in the COX modem?

As I said, I have had this problem in the past with my old COX modem and with different routers, but now its impractical to reset everything to factory defaults every time it happens.