Do you get an error message when you try to access the channels installed on your Roku device? Could you tell us how your Roku device is powered? Is it plugged into the TV's USB port or a power outlet? In some instances, the TV's USB power is insufficient to power the device. Running your Roku device with insufficient power can result in instability, crashes, and other unpredictable behavior, even if it appears to be operating normally.
Using the included power cord and power adapter, we suggest plugging your Roku into a working power outlet in the wall. Powering it through a power outlet in the wall has the additional advantage that your Roku player will not need to power up every time you turn on your TV. This means your Roku player will be up and running faster than it would be connected to a TV.
Please keep us posted and we'll continue assisting you from there.
If you are still unable to play videos from one channel after attempting the suggestions by @RokuLianna, videos from other channels play fine, we suggest that you to 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 the channel developer.