When I am watching live TV, I usually see the commercials during a commercial break, but sometimes I just get a screen that says "Commercial break in progress. Programming will return shortly." Why does that happen? I'd rather see the commercials than 2 - 3 minutes of stupid dead air.
That is a point where there is supposed to be a local commercial inserted. It seems as if the XFinity stream service doesn't support that, or maybe is just not properly configured for that channel.
What channels (use names, not numbers) do you see that on? Most national networks will have generic national commercials, but most local stations or cable companies will do inserts over them at specified times.