Up until I bought the Roku, I had a video game console plugged into the same HDMI port on the TV and I never had this problem. It was after I bought the Roku and unplugged the game console to make an HDMI port available that the problem started. So I think it's safe to say the roku is somehow causing the problem.
Was there ever any resolution to this? I just got an Ultra and I'm having the same problem. It worked perfectly with my fire stick. I wanted to switch over to Roku so I went with the top-of-the-line model and it's not working. My TV speakers are weak and sound bad so I got a Yamaha bar a few years ago. The bar worked perfectly with DirecTV and Fire Stick but Roku jacks up the ARC for some reason.
Nope! No solution. I ended up calling Roku support. Was on the phone for 30 minutes, and they said it was an issue with my LG TV. So I called LG, was on the phone for 30 minutes, and... surprise! They said the problem was with the Roku.
As of now, I am having to manually power on the soundbar every time I turn on my TV (so long as the Roku is connected.) It is not difficult, but certainly an inconvenience, especially given how much money we pay for TVs and audio equipment.
