I have experienced the same thing starting about the same time. I have gotten it on every show or movie to some extent. I had not tried resetting my box, but will try that and report back.
This problem had been a problem in past years, but had all but disapeared until recently. Can anyone else report either having or not having this problem to see if we can see how widespread On Demand pixelation is?
It's been about two weeks or so that pixelating/freezing issues have started on 3 of our TV's, but not all of them. I have a mini DVR box in my room that 3 TV's are hooked up to. Two of the TV's running thru that splitter are absolutely fine but one is experiencing severe pixelation issues. 3 other TV's are running thru a splitter to a DVR box in the basement and 2 of those TV's are experiencing pixelation issues, one is worse than the other. I restarted the boxes today so I'm not sure what the outcome will be. It does seem to happen when more of us are using their TV/devices. Could it be a traffic issue (too many devices in use?) or are some of the set top boxes not getting a strong signal and need replacing? Going to try unpluggin everything first - so haven't called Comcast just yet.
I watched a couple of On Demand movies after my post on June 23rd. One was before I rebooted my cable box and one was after. Both movies had only a few minor instances of pixelation. So it seems that the pixelation issue was mostly gone by the time of my first viewing. Rebooting my box seemed to have had no effect in my case. We will see what happens in the future though.