The Roku Channel is temporarily unavailable on Samsung TV
On my Samsung QN90AA-50 using the Roku app, none of the on-demand content can be viewed. It shows the Spinning Circle of Serenity until it finally times out. Most of the live streaming channels show a black screen with the program information and the transport bar (no sound either). Every now and then a commercial will show and then back to the black screen. A few streaming channels like This Old House Classic still work, but not the current This Old House channel or the Dateline channel. I have deleted and re-installed the app twice with no change. Other streaming apps work fine (SamsungTV and Amazon). The app worked fine a month or two ago when I last used it.
Lost BBC America Channel
I am having the same problem. Followed your instructions, deleted channel, went to settings and restarted the Roku from there, reinstalled BBC America, and still have the same problem as described by OP – channel opens, stutters/flashes a couple times, circle shows slowly loading and after a half-second flash of content squares, goes back to the home screen.