I was finally able to clear the problem (for now) on all but one of my Roku devices and (I believe) deduce the root cause of the problem-- stale login data on the Comcast servers. Definitely not stale data on the Roku devices, as factory resets/power cycles were performed.
A couple days before my "outage" my brother logged onto one Roku with his account to watch his To Go channels. Fine, no problem, when he was done I successfully logged the Roku back in with my account. Two days later, all Roku devices were logged out, with only one able to log back in. Finally (with nothing to lose) I decided to log back into his account to see what might happen. After logging out his account from the Xfinity Stream app on the Roku the problem cleared on this Roku as well as 2 others. It still persists on one last Roku, probably because somehow it is still picking up the stale login in the network. As such I am concerned that the problem may reoccur on the other devices if/when they log out again.
Independent of such workarounds, this is still a problem in the Comcast network. Every new login should be a clean one, especially after all in-home Rokus/phones/PCs have been logged out of Xfinity and then logged back in. None of these past logins should persist in the network after a new login is performed.
