Thanks for reaching out here in the Community!
In some cases, removing the affected channel and then re-installing them helps. 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 the issue persists from one channel after attempting the suggestions above, videos from other channels play fine, contact the channel provider's customer support team to report the issue and get help. Channels on Roku are maintained by the channel developer themselves. In this case, there's likely an issue within that specific channel that needs to be addressed with an update from them.
We appreciate your understanding.
All the best,
Roku Forum Moderator