We're not currently aware of any known issues with Fox News on Roku devices. I tested the channel here and am not encountering any troubles.
I'd recommend restarting your Roku device, then trying again. If that isn't resolving the issue, try removing the channel from the Roku home screen by navigating to the channel tile, pressing the * key on your remote, then choosing 'Remove channel'. Then, go to Settings>System>System restart, and reboot your Roku device. Once it starts up again, add the Fox News channel back once more and log in with your TV provider again.
Please let us know if that helps clear up the issue you're seeing. If not, I'd recommend reaching out to Fox News support directly to report the issue you're running into with their channel, and request any additional support they may be able to offer.
Roku Community Manager