I had the same issue. In my case it was being caused by the VPN running on the FireStick.
I added an exception for 'The Roku Channel', and now it works fine...
I use IPVanish to utiloze the "special apps" on my Firestick. I never thought it or any VPN would block the Roku app. I disconnected my VPN connection, jumped back to the Roku app, and playback was no longer hindered. Thank you for sharing that solution. Heck, I work in IT and I missed that part of troubleshooting the issue. I always have IPVanish running.
Thank you!
