In my experience, that's an indication that the device has died and needs to be replaced. You can swap it for a new one at your local service center (https://www.xfinity.com/support/service-center-locations/) or you can have a tech swap it for you free of charge.
You can try a factory reset (hold the button in the pinhole on the rear of the device for ~30 seconds.) That may fix it temporarily. Either way, swap the device ASAP.