Internet not quite right after purchasing NetGear Nighthawk CM2000 [Resolved Jan 28, 2021]

I recently signed up for Xfinity. I purchased the Netgear Nighthawk CM2000 (modem only, no voice or WiFi router included), hoping to not rent the xFi Gateway anymore. Initially, I took out the xFi Gateway and plugged in the Netgear modem.

The indicator lights were all white and looked fine - though the "download" light is always blinking white constantly, while the "upload" light is almost always solid white.

However, I started to run into issues.

1. Only a few devices could work via the LAN port of the Netgear CM2000, while others didn't. (I inferring it was because those devices had a max Ethernet speed of 100 Mb/s, and anything capable of 1,000 Mb/s failed to connect via Ethernet.)
2. (Though not directly related,) I set up my own router (Linksys WRT3200ACM). However, my own router failed to pick up any internet connection at all during the whole process.

This is all sort of strange, because a technician had already came in about 2 days ago to set up the xFi Gateway, so no other coaxial connections should be loose or anything like that.

I had some more "detailed" issues? Definitely not sure if these could be fixed by a technician or not.

• Additionally, when I accessed the modem at 192.168.100.1 in my browser and explored the Event Log under the Advanced options, I noticed a constant stream of messages with "(Critical (3))" priority about: T3 timeouts, "Ranging Request Retries exhausted", and "No Ranging Response received". The messages keep cycling through in this order. (I'm not sure if posting the raw log info is extremely sensitive information.)
• Lastly, under the Basic options, the downstream channel power values are rather high and not under absolute values of 7 dBmV (somwhere between 8-11 dBmV), while only 2 out of 8 upstream channels have power levels of 39-41 dBmV (so, somewhat normal values) - according to some nebulous source while web searching. (Also I wasn't sure if posting this info was too sensitive.)

I'm sort of getting desperate at this point, because I had double-checked to make sure I purchased a compatible modem for Xfinity, and I've read other stories (some on them marked resolved and others not) on how some poor souls even went out to buy duplicate modems (in case there were defects) or entirely different modems to no avail, only to find some issue that couldn't be fixed by doing what they did.