CNN signal was sporadic and now the channel is unavailable. Seems funny that the channel that gave objective reporting on net neutrality is now being inhibited by "Big Cable". Got no help from tech support and refreshing the gateway was of no help. Gonna have to switch providers.
Unless you get a "Not Authorized" style message, then it sounds more like you just have a signal issue affecting the frequency used for CNN. Other channels may be affected, but you may not watch them, so not notice.
Since Comcast seems to pack the same sets of HD's together, and if you are talking about the HD version, try checking: AMC, Disney, Freeform, Golf, Science, Hallmark, HSN, Investigation Discovery.
The CNN channel works fine for me here in zip code 05478. I'm sure that if it was being 'blocked' or 'inhibited' we'd see more than one customer reporting it here.
Try getting CNN on the lowest channel number which would be SD version. That channel should be working. The RF interference usually happens around certain HD channel frequencies.