I also have had the same problem on many different hardware and software platforms. Being in the tech field I really don't think it is customer related equipment.
It's hard to troubleshoot a random problem and to me this one seems random. It doesn't seem to be anyone commercial that sets it off. I do think pausing a show and restarting it can cause problems. I have done all kinds of troubleshooting cause my kids love the service and really haven't come up with anything great except what I have listed below. If I don't do as listed below and just close and restart the program it is still in the ad loop.
MY SOLUTION:
Once the program starts messing up, I have to exit and go back to the xfinity TV page. Scroll down the page where it shows my history of the shows I have watched. Each show I have watched is pictured and has an X on the top right of the box. Click the X to delete the show out of my history. Now go back to the top and select your show again.
It starts the show all over which is a pain, but it stops the crazy ad loop. I have been able to skip ahead with some luck but sometimes it causes the ad loops all over again and I have to start this process all over again. Sometimes I have to skip just enough ahead of the ad loop which causes me to miss some of the show but at least it works.
So in my conclusion Comcast, Xfinity, Time Warner, someone has a problem with there streaming server and injecting ads into them. I was hoping to come here and find a solution to my problem since it has been going on for so long but based on what I'm seeing I will not be holding my breath on that one.
Guess take it for what it is and Good Luck out there!
Does Joe even work for Comcast anymore? Just wondering...............
