I have been experiencing the same issue with Spectrum, my CM1200, and old firmware. With my CM1200 I experience between 2% and 20% packet loss, depending on the time of day (it seems to directly correlate to Spectrum network congestion on my local segment), and when I'm not dropping packets, my latency to IP addresses within 100km of me fluctuates wildly (between <10ms and ~900ms). Spectrum technicians have visited a few times and checked the lines all the way from my cable modem to the first upstream Spectrum device, and found no issues, so it doesn't appear to be a layer 1 problem.
When I initially spoke to Spectrum support, they said that the CM1200 wouldn't work on their network (despite the fact that mine had been working just fine until they made a change on their backend). When I pointed them to this page on the Spectrum site which lists the CM1200 as a modem that Spectrum recommends for Internet speeds up to a Gig, their story changed, and I got escalated to an engineer.
From looking through my network logs this began at the same time that Spectrum enabled OFDMA in my region. This issue has been fixed for a while now in CM1200 firmware, as @ssherm01 points out. Whoever at Spectrum said that they don't update customer modems, though, was misinformed. Spectrum controls the firmware version on cable modems on their network, whether those modems are owned by Spectrum or the customer. I've even heard tales about customers getting test CM1200 modems from Netgear that were running newer 2.x firmware, and these test modems worked great with Spectrum for a bit until they were downgraded by Spectrum to V1.02.01 (at which point they began having the issues that you're experiencing and that I experienced).
The Spectrum engineer with whom I spoke spent some time explaining to me exactly how they rolled out firmware to customer modems (including customer-owned modems), why they wouldn't allow customers to update the firmware on their own (personally-owned) modems, how they kept customer modems "in compliance" (including auto-downgrading firmware), and much more. In fact, the only thing he didn't seem to have any idea about was when Spectrum was planning to update the CM1200 firmware from V1.02.01 to something newer, or if Spectrum was even in the evaluation/testing process for such firmware. This Netgear page indicates that Spectrum is the only provider still on V1.anything for the CM1200, so I'm not optimistic.
For now, I am temporarily using a Hitron EN2251 that Spectrum sent me as a troubleshooting step, and I'm no longer seeing the constant channel lock errors, packet loss, jitter, and other problems that I was getting with the CM1200 after Spectrum rolled out OFDMA. I'm checking the Netgear page once a week to see if Spectrum has finally updated the firmware, at which point I'll give my CM1200 another shot, but meanwhile at least I can use network services again that are sensitive to jitter and packet loss.
To me it seems like this is entirely in Spectrum's court to fix:
- Spectrum lists CM1200 as a recommended modem
- Spectrum deploys OFDMA, which effectively breaks that recommended modem
- Spectrum won't udpate the older firmware with a known fix for the known service issue they caused with that recommended modem (firmware that all other ISPs have already upgraded)
...so Spectrum should provide an acceptable workaround to affected customers until Spectrum has resolved #3.
