Watching TCM through our Apple TV using the WATCH TCM app; TV provider is Xfinity

We subscribe to TCM through our cable provider Xfinity. We usually watch TCM on our Apple TV through the downloaded app Watch TCM. Often, when we try to watch a film on Watch TCM, we are directed to sign in to our Xfinity account and enter an authentication code. This is a hassle but we comply. Recently, we have simply been unable to watch TCM through the Watch TCM app no matter how hard we tried. We have logged out of the app and then signed back in, we have changed settings on our Apple TV to make sure it knew that our TV provider was Xfinity, etc. Each time it accepts our login and says we are set to go but when we try and PLAY the film, the next screen is a black screen and it doesn't move on from there. We have even tried to log in to Watch TCM from our mobile phone. We can log into our account on the phone but we can't play a film.

Xfinity seems as baffled as we are. We would be grateful for any advice as to how we might solve this annoying first world conundrum. Many thanks