I have several Roku TVs and the Apple TV has suddenly stopped working. I now get "Network Unavailable" errors on every device. Apple TV works fine on my iPad and laptop. I have updated drivers on all my Roku devices. I have reset my router. The problem appears to be specifically with Apple TV through Roku. Anyone else having this issue?
Try removing the channel 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 player starts up again, add the channel back once more.
In addition, have you tried signing out of the Apple TV channel and then signing back in again to see if that helps the issue you are experiencing?
Please keep us posted what you find out and we will be able to assist you further.