Hey kkuenne,
Welcome, and thanks for the post.
If the issue persists on one channel after attempting the troubleshooting steps and videos from other channels play fine, contact the channel provider's customer support team to report the problem and get help. The channel developers themselves maintain channels on Roku. In this case, an issue within that specific channel likely needs to be addressed with an update from them.
Please keep us posted if there's anything else that we can do to assist you.
Cheers,
The Roku Community Team
