There have been assorted problems with commercials for more than a year I'm sorry to say, but I personally haven't seen commercials loop more than twice. There is a thread started by the Comcast suppport people specifically for users experiencing problems with commercials. http://forums.comcast.com/t5/XfinityTV-Website/Ad-Issue-during-Video-Playback-on-http-xfinitytv-comcast-net/td-p/2064840 Please read the first post by ComcastJoe and reply with all the details that he requests and hopefully something will be done.
As an alternative, if the commercial problems get to be too much you can always go directly to the networks own website and watch from there. Almost all networks i.e. ABC, CBS, NBC, Fox, the CW, FX, HBO have streaming available from their site and they don't appear to have the same issues with commercials that the Xfinity site does.
- Norm