Unplug the optical cable from the soundbar, let me know if you see the little red light on the back of the TV at the optical cable.
I have also started getting this since updating the firmware the other day on my Q60R. I output my audio using optical cable to my receiver but have the sound setting on the TV set to TV as that allows audio both to the TV speakers and out to the optical simultaneously. Setting it to just optical is not an option as I don't always want to turn my receiver on. I have disabled ARC on HDMI 4 as I don't use that.
I simply unplugged the optical cable from the TV. It would only be used for the SmartTV features to output audio from the TV to the receiver, but since I have a FireStick, I don't really need the SmartTV anyway. That's the only way I could get the message to stop appearing.