Home Theatre volume control

Hi; I have a Samsung smart TV & have my Roku Ultra's HDMI cable plugged in to a TV HDMI port. I also have a Samsung home theatre system which has an HDMI cable connected to it's HDMI output port. The other cable end is connected to the TV's HDMI-ARC port. have followed instructions for setting both TV & Roku audio settings such as HDMI-ARC & HDMI CEC. I have managed to have the Roku turn on both TV & sound system along with controlling the sound system volume with the Roku remote. However, my Roku hub's LED indicator light randomly flashes without touching the remote. The next time I turn the TV & sound to "ON", I can no longer control volume with my Roku remote. There seems to be an audio issue that the Roku does not like. When resetting audio settings & use my sound system's remote for volume control, the Roku's hub indicator light stays on as it should. Any ideas??