The issue I experienced was on a FireTV, using the Roku App.
Roku customer service was no help. Their focus is sending stock instructions regard a Roku device. Although I own a Roku device, I was not using it on the FireTV; the problem was with the App. The Roku App was the only App not working.
After signing in and out of my account and deleting and reinstalling the App several times, in different combinations, I gave up.
I reset the TV to factory settings, reinstalled all my Apps, and the Roku App finally worked.