Even though the signal stats looked o/k at that snapshot in time, the error log entries confirm that something is going on. Perhaps there is noise ingress into the line(s) somewhere.
There are other signal stat figures that can't be read by the modem. They are the "Upstream Rx Power" (Upstream Receive Power Level), the "Upstream SNR Ch." (Upstream Signal To Noise Ratio), and the "Upstream ICFR" (In Channel Frequency Response). These are as equally important in diagnosing connectivity issues as are the modem's stats.
I'm going to escalate your issue to the Comcast corporate employees that are available to these boards. They can check the CMTS (Cable Modem Termination System) for any real time degradation and / or error reports, see your node / cable plant and modem health, and see whether or not everything is in the green zone. They can also see a history plot for the modem and poll for those upstream receive signal stats.
You should get a reply here in your topic. Good luck !
Thanks for posting to the Xfinity Forums to make us aware of your connection issues. I can imagine how frustrating this would be. Let's find the problem and get this fixed as soon as possible. I'll start by checking your signals and for issues at the CMTS. Can you please send a private message including the full name as it appears on the account and your full name if different? To send a Private Message, please click "Comcast_Support” and click “send a message".