Try removing the channels from the Roku home screen by navigating to the channel tile, pressing the * key on your remote and choosing 'Remove channel'. Then restart your device from Settings>System>System restart. Once your Roku TV starts up again, add the channels back once more. Does this clear up the issue you are seeing?
As a last resort, we would recommend removing the channels that you are having issues with, then trying to perform a factory reset on your TV. Then once your TV has been set back up, try adding the channels back to see if the issue is resolved.