How come I can watch the Paramount Network on my TV, it's in my current channel lineup, but, if I try to watch anything On Demand from Paramount Network via the app it says I need a subscription?
https://www.xfinity.com/support/cable-tv/online-tv-through-partner-sites/ does not currently list 3rd party as available nor unavailable. maybe the link web page will be updated soon. the contracts determine what the vendor (like paramount) provides to subscribers.
It's off and on. One day it'll be there, the next it's not. It sounds more like the issue people are having with their channels mysteriously disappearing on the app.