My 2cents: Install PingPlotter (free trial for 14day) on your computer with wired connection to your router (also try cable modem directly bypassing the router), run for 48hr to collect packet loss data so it will give you some hints where the problem is.
Each ease could be different.. My case happens to be node saturation. I agree that the Cox internet in the Chandler area has been VERY unstable in the past few days. Today is another day with service outage (4th time in the past week).
Another option, since Cox over sold your node and knowingly sold services they do not have infrastructure to actually support, is file a complaint with the AZ attorney general. https://www.azag.gov/complaints/consumer