modem snr less than 30dB on many channels

I have a 8x4 modem... Downstream SNR less than 30db on most channels.   And many uncorrectable errors.
A few days ago, it got so bad that speedtest fell to less than 1 Mbps. And became impossible to do video streaming.

I don't know if anyone actually worked a fix but it recovered after a few hours and I saw SNR go up to 33 or more on all channels.  And speedtest went back up to about 40Mbps (I pay for 50Mbps service.)

Today it has deteriorated back to SNR 29 on most channels.  But speedtest still running well about 30Mbps and no trouble currently with video streaming.

Does COMCAST/XFINITY do any proactive monitoring to discover and fix these issues?  
Seems to literally vary with the weather - bad on cooler and wetter days....

Who do I call to really get this looked at?
In my experience, the telephone staff only knows how to respond with simple scripted answers -- like "Try restarting your modem" (I've done that!).