I'm beginning to wonder if this may be at least partially caused by something on my end.
I have a pair of Netgear MoCa bridges: one between my modem and the wall outlet and the other off a splitter near my TV.
Today my upstream signals took a major dive and my modem lost sync and got stuck trying to find an upstream channel. At the same time my TV signals crapped out and I had a SNR of 29 on one my lower frequency channels (not enough to lose picture, but I was getting a lot of corrected errors).
I called into Comcast and they told me all my neighbors were online so I tried disconnecting my modem and hooking up an old DOCSIS 2.0 modem. That wouldn't lock either. I then bypassed my Netgear MoCA bridge and the modem locked and actually got a 44 dB upstream power level. I then placed the Netgear MoCA bridge back in and the modem still locked with the upstream power level about 45 dB. I checked my TV downstairs and the signal levels looked good there too after this.
So it looked like the MoCA bridge was somehow corrupting the upstream and low frequency signals a lot and the higher frequencies a little, but that makes no sense since the MoCA bridge is supposed to operate at frequencies greater than 1 GHz and has worked fine for a few years now. What's odd is that on October 9th, when I first started having problems, the Comcast tech measured the signals before and after the MoCA bridge and they were basically the same. Also I don't know why a MoCA bridge upstairs would cause problem with the TV downstairs
I suppose that it could be a coincidence that the signals got better when I disconnected and reconnected the MoCA bridge, as the time it got better was around the same time it got better yesterday, but that seems suspect. I also have 3 other MoCA devices, none of which I disconnected to get things working, though the one I disconnected is the "Master/Controller".
Currently my modem signals (going through the MoCA bridge) have been steady for the last 3 hours at:
Downstream
Channel Frequency: 657001587 Hz 651000244 Hz 662998413 Hz 675000977 Hz
Modulation: 256 QAM 256 QAM 256 QAM 256 QAM
Signal strength: 2.8401 dBmV 2.7655 dBmV 2.7906 dBmV 1.9403 dBmV
Signal noise ratio: 37.936 dB 37.356 dB 37.936 dB 37.356 dB
Upstream
Channel Id: 9 7 8
Upstream Frequency: 22000200 Hz 36200144 Hz 29400296 Hz
Upstream bandwidth: 3200000 Hz 6400000 Hz 6400000 Hz
Transmission signal strength: 45.5000 dBmV 46.5000 dBmV 46.7500 dBmV
The downstream signals are what they were yesterday, but the upstream power levels are lower.