Netgear CM1200 is 32×8 Downstream Light: Blinking Green (Scanning for additional downstream channels)
I don't know why the Downstream would be blinking because you have 32 locked channels.
Your Upstream, however, only has 4 Bonded Channels. I'd assume...due to gigabit...you should have 8. Your Upstream Light should be blinking.
dave9 would be the best source but I think the OFDM(A) channels are your overall circuits. These circuits are then divided into separate channels: 32 and 4. Therefore the overall circuits wouldn't be individually locked. I could be wrong and sure I am.
I guess a good question: why don't you have 8 Upstream channels?
As far as I know, very few areas have 8 upstream channels. Most have 4, and a few have 5 (really more like 4 1/2) due to congestion. Gigablast only supports up to 35 Mbit upstream so 4 channels is more than enough for that. As you pointed out it's odd that the OFDMA channel isn't locked since I think all of Cox is on DOCSIS 3.1 now. That's something a tech would need to investigate. As mentioned, it could be caused by noise issues in the 300 MHz band used by OFDMA.
Moral of the story is that Cox always blames the modem because it's a quick way to get customers off the phone and keep call times down. And very rarely a modem does break down. But it's almost never the modem. It's a good idea to keep up with new technology and upgrade your modem every few years but most of the time when Cox blames the modem they're just plain wrong.