I agree with Tony that a FR would be worth a try, as I had a very similar problem that looked to all intents and purposes like a local circuit issue,which even my BQM tended to support, but when The Swansea Team member queried the CMTS he found no issues, and suggested a FR which against logic rectified the problem. Probably the SH2 firmware just needed a boot up the backside.
With the missing channel, and poor SNR on adjacent channels I would not rule out a loose connector, so for the sake of a 5min check worth a shot. The evidence posted at least warranted further investigation \ engineer visit.
I find it hard to believe that VM cannot take the evidence posted on board and not query the CMTS\local circuit for issues, I take it they have the tools at their disposal like their Swansea ex-colleagues.