Unstable Internet Connection

I bought a new router and modem about 3 months ago. I have a R8000P Nighthawk X6S AC4000 Tri Band WiFi Router and a CM 1200 Netgear Modem. My modem receives internet from Cox via wired connection, and then my router is connected to my modem via a yellow Ethernet cable. All of my devices connect wirelessly to the internet except for two. These two devices are connected via a wired connection into the router.

Recently, I've been having internet connection issues. Essentially, my connection to the internet comes and goes. It will work for a few minutes and then stop working for a few minutes, on and off. During the brief periods that it is working, my speeds are noticeably slower. I've noticed that when I have this issue my upstream or downstream light on my modem will flash repeatedly. 

I've contacted Cox about the issues over a dozen times. They are adamant that the issue is not on their side, and that it is likely an issue with the hardware. Given how new my hardware is, I am skeptical. I've had Cox reboot the modem remotely several times. Sometimes rebooting helps, but only temporarily. I've been scanning the forums for a solution, but have yet to find one that has worked for me.

Any ideas on what I can do?

I've attached a copy of my cable connection log in case that helps.