... XFinity keeps saying the connection is fine ...

It is not. Several channels have out of spec SNR (too low).

Network connection problems like this are often due to poor coax connections or damaged coax cable, usually in or near your home. Running the cable through a surge protector, a defective splitter, or too many splitters can cause signal problems as well. If there is an amplifier in the line make sure it's getting power. 

If you want to troubleshoot this yourself, please see Internet Troubleshooting Tips.

If you can't find the problem or you'd rather have Comcast take care of it and an employee does not respond to your message here, call them at the phone number on your bill or 1-800-Comcast, or use one of the options on https://www.xfinity.com/support/contact-us/. It's not likely they can fix the problem remotely. 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 ($70-$100) 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.

Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.

There is a connection quality problem on downstream channels 8 thru 11. The SNR's are too low / out of spec. And there are a large number of uncorrected bit errors. This is typically caused by spurious noise at those frequencies leaking into the coax line(s) somewhere. Have you first tried rebooting / powercycling the modem ? This may result in it picking up and locking on to a new / different set of downstream channels that may not have that problem.

Please also post the upstream channel power level values.

@bvkiran Good morning! Thank you for taking the time to reach out to our Community Forums Team for assistance with your internet connection. Based on what you are sending over, I can see how this would be a concern. I would be happy to take a closer look, and get you in the right direction for a resolution. Before we begin, can you tell me if you have tried any troubleshooting steps on your end? This way we don't repeat the same steps. Also, do you have any splitters, extenders, or any devices of that nature connected to your network aside from your modem? 

@BruceW 

Sorry Bruce. I didn't see your post when I posted my response...

@bvkiran 

Did you get a chance to try any of those tips that @BruceW gave you ? Or even just start with a modem reboot operation that I suggested ? Also, please post the upstream power level values that I previously requested.

The upstream power is out of spec too. Here's some stuff that you can try that may or may not apply;

In an effort to try to obtain better connectivity / more wiggle room, check to see if there are there any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/re-configured. Any splitters that remain should be high quality and cable rated for 5-1000 MHz, bi-directional, and no gold colored garbage from Home Depot, Target, Wal-Mart, etc. Splitters should be swapped with known to be good / new ones to test.

Also check the coax cable for any damage such as cuts, nicks, abrasions, kinks, sharp bends, etc.

If there aren't any unneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two-way splitter connected directly off of the drop from the street / pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then check for and clean off any corrosion / oxidation on the center wire and put them back together again, then perhaps it's best to book a tech visit to investigate and correct.

Bear in mind that if the premises facing techs can not find or fix a problem at your home, it is they who are responsible for escalating it to their line / network / maintenance dept. techs. The problem may lie beyond your home in the local neighborhood infrastructure somewhere but it is their S.O.P. to start at the home. And if the problem is found to be on their side of the demarcation point, there will not be any charge.

Good luck !