can't load xfinity stream on amazon fire tv stick

In the past I've used Amazon Fire TV sticks to watch my Xfinity programming on the Xfinity Stream app, rather than rent a cable box or when traveling watching my Xfinity programming.  Lately when updating all my fire tv firesticks, the Xfinity Stream app is "available" in the Amazon appstore and sometimes in the cloud, but when trying to load, it says "app not found."  Any reason why?  I can load it on my Roku streaming stick, why not Amazon fire tv devices?