The downstream signals look OK, but the upstream levels are borderline/too high. And the error log "Dynamic Range Window" and "Commanded Power Exceeds" errors both suggest an intermittent connection to Comcast's network affecting the upstream channels. If you want to troubleshoot this yourself, please see Connection Troubleshooting Tips. Problems with Internet service are often due to poor connections between your equipment and Comcast's network, usually in or near your home. If you can't find the problem or you'd rather have Comcast do the troubleshooting, call them at the phone number on your bill or 1-800-Comcast, or or use one of the options on https://www.xfinity.com/support/contact-us/. It isn't likely they can fix this remotely, and if not insist they send a tech out to identify the cause and correct it. If the tech finds bad coax, splitters, amplifiers, or connections in your home (even if Comcast originally supplied them) you'll probably have to pay for the visit unless you have their Service Protection Plan (https://www.xfinity.com/support/articles/service-protection-plan, closed to customers that don't already have it). If the trouble is due to a faulty Comcast rental device, or anything outside your home, you shouldn't be charged.
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