This is why the Xfinity Stream app and Xfinity Instant TV are garbage!
In beta for over a year-and-a-half, the Xfinity Stream app is sorely lacking in any kind of technology that we've become accustomed to in the last 10 years. You cannot see an image when you fast forward, if you fast-forward too far and try to rewind right away it screws up and gets confused. Then there is the dreaded error: TVApp-00306. when I had cable boxes in the house I never received this error. I therefore must conclude that it is Xfinity instant tv and their cloud DVR. With literally dozens of examples to look at Xfinity still gets it wrong! I am not addressing this to anybody at Xfinity because I know you're all useless when it comes to resolving issues like this. As a matter of fact there is a thread out there on this very for that states that this issue has already been fixed. Funny how only Xfinity employees seem to think that that is the truth. As I write this I'm staring at a screen with that error on it. and I can tell you this, the recordings that are on my DVR right now will never play regardless of if they fix the error or not. I restored one of my deleted recordings and it played fine. All I can say is that Sling TV, YouTube TV, and DirecTV don't have these problems. And Comcast has more money than all of them combined. Big Shock! Gee I wonder what I'm going to do next.
the stream app works fine. the issues you describe with the roku beta stream channel (roku?) may mean you are not accustomed to using beta software/programs. complaining about non-yet-existing features is not helpful. If you do not like using the beta service simply use a set top box or the stream app on authorized devices (iOS/android for example). Comcast does not charge for the add-on benefit of having stream available to smart devices.