IPTV stuttering and high uncorrectable errors in Motorola 8600 config

I'm using an IP TV box and started having a lot of stuttering in the streaming to the point where it is unusable.

I initially suspected a service issue and swapped for a different service provider, that didn't help. I also swapped out the hardware (IP TV Box) and got a new one and that didn't resolve the issue either. I took my box to my neighbor and that worked fine with his service. He brought his box over and that had the same stuttering issues in my house. So its something in my house - my Xfinity connection, cable modem, router, switches, cabling, or something specific to IPTV.

I've eliminated the IPTV box and the IPTV service already like I said - tried a new service and a new box and tried my service and box at my neighbor, their box and service in my house (which shows the same problems).

I also eliminated the indoor ethernet cabling and switches by bypassing all of that (connected the IPTV box directly to the router that's right after the modem (Motorola 8600). 

I eliminated the Wifi router by connecting the IPTV box directly to the cable modem and rebooting both. 

I looked at the cable modem config page and it showed a large number of uncorrectable errors for about 10 out of 32 channels. I called xfinity support and that was a total waste - the person I talked to didn't know what an IPTV box was. She did some basic troubleshooting (rebooted the modem) and then said it all looks fine, she suggested I contact the IP TV box manufacturer and when I told her the box works (because I swapped it for a new one and mine works elsewhere) she then moved to asking me to contact the cable modem manufacturer since I'm using my own cable modem. Does this really sound like a cable modem problem? Based on what?

I'm suspicious its something with the signal coming into my house but don't know how to diagnose that without xfinity help (and that doesn't seem to be coming). The lack of help is frustrating and I'm on the verge of switching to another ISP.

This is after a reboot a couple of minutes ago.