CM1000 Losing Connection and Rebooting Constantly (Cox)

I recently upgraded my Cox internet package to Gigablast, and as such, I had to upgrade to a DOCSIS 3.1 modem. I went with the CM1000 because I was running the CM700 prior, as well as having an R7800 Nighthawk X4S router. The CM700/R7800 combo worked quite well and I never had any issues with either.

However, when I got the CM1000, installed it, and updated the modem information on my Cox account, the modem would reboot every few minutes.

I figured out it would reboot immediately when I tried to connect my phone or laptop to the R7800's wifi and would have a semi-stable connection either when I have it directly hardwired to my desktop or I don't try and connect any other devices to the network. I haven't figured out why the connection resets when connected via hardline due to it cutting out at random intervals for no related reasons.

Also, even when the network is connected, the taskbar internet icon shows  "Network - No internet access", despite being able to browse the web and play online games just fine. While the connection is stable, I get about 900-950Mbps down and about 37Mbps up (according to speedtest.net).

I had Cox send out a technician, and he upgraded my coaxial cable and ran the line directly from the splitter box on the building to my modem. Despite the upgrade, the issue persists. He said he's never seen something like this and recommended I return the CM1000 for a new unit. I'm not against doing that, I'd just like to see if I can get this one working so I don't have to go through the hassle of returning the damn thing.

I've updated the R7800's firmware to 1.0.2.58, and the CM1000 firmware is 3.01.04, so that's not the issue (I think). Still, not sure if it's just the R7800 not being able to handle the data load or if there are just some weird incompatibility issues between the CM1000 and the R7800.

Any help would be appreciated. Thanks.