I signed up for Discovery+ through the Roku Channel and nothing will play. I highlight the episode (old or new) and press the "ok" key. It says loading for a split second and then goes back to the highlighted episode. All other streaming services work (Netflix, Disney+, ect) as does live tv.
In some cases, removing the affected channel and reinstalling them may help. To ensure the process is successful, make sure to restart your device before adding the channel back in. We would recommend doing this from the Settings menu by navigating to Settings > System > Power (If you do not see a Power submenu, skip to the next step.) > System restart.