I recently had the same problem. Was watching a CNN program "On Demand" one day and the next day could still get "On Demand" but instead of going right to the program when I clicked it, the process of switching would lag and I'd get a message to call Xfinity, unplug the unit for a minute, and/or go to Comcast.com/help. I also had messages on my account online that warned of a Comcast outage in my area. Nevertheless, I wanted to know if my problem was unique. So first one repairman tried the usual fix, a new box, and new connectors, still the same. He left and returned with another repairman and they proceeded to replace ALL the cable everywhere, add new connectors again, new splitter, and finally out to the pole. Same thing happening only now it states "BUY" when I try on demand like I have NO subscription for any of it even regular TV shows "On Demand." I felt sorry for the repairmen because I believe it's a glitch in the code. Of course they can send hit after hit like the "refresh" tab on my laptop works, but if the code is wrong, I'll still end up with "BUY" instead of "WATCH."
So Comcast you might wanna look at the code someone typed in for all of us when we ordered our subscriptions. Because it either changed or someone changed it so we are no longer allowed to use and view what we're PAYING FOR! .I have one more thing to say, and that is if you can't fix something like this, why is we're supposed to trust that you can provide security for our homes?