Posting here based on advice in this thread.
I can navigate throughout the CBS channel with no problem, on Roku or Web app. But actually playing any episode seemingly tries to load forever. On the Roku, the player shows 13%, then 33%, then goes until it gives up. Web app seems to do the same. Other channels are fine.
Other reports in the thread above have indicated that this appears to be unique to having PMS 1.3.x on Linux.