Thanks for reaching out here in Roku Community.
We're here to help. Have you tried to remove the channel and see if it helps? If you haven't tried it yet, you can remove the affected channel and re-install it. To ensure the process is successful, 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.
For detailed instructions, refer to this Support link: How do I resolve channel playback issues?
If you still can't play videos from one channel but can play videos from others, contact the channel provider's customer support for help. The channel developer maintains the channels on Roku, and there may be an issue that needs to be addressed with an update.
Keep us posted on how it goes.