I have the same issue. Has anyone had any luck resolving this issue? I called the support line and the best advice they were able to give me was to mail me new firmware. I haven't received the package yet, but not sure how she determined that would magically fix it. Unless it's a known issue and she didn't want mention it.
Background. My Samsung TV (65" NU8000 Series) and MS650 Soundbar were connected fine after Best Buy installed it for me. (I had to troubleshoot the TV because after using it for 3 weeks, there is a dead pixel row across the screen! During the troubleshooting the support person told me to reset and disconnect everything--the TV, the Soundbar etc. After 40 min of instructions, she determined it's a dead pixel issue, which I told her during the first minute of our conversation! When everything was turned back on, the soundbar shows D.IN and the TV sound out goes to TV Speaker by default. When I change the sound out to the soundbar and then change the source on the soundbar to HDMI, the TV out source "jumps" back to the TV Speaker out. If I try the other way around: change the soundbar source first and then the TV out source to soundbar, then the soundbar "jumps" back to D.IN. Long story short--HDMI output no longer works.
Vent. It's mind boggling to me that the product from the same company don't talk to each other and the soundbar is not exactly very complex system, so it should be easy to test before shipping. I've had Samsung products for over a decade but in the recent years I've been very disappointed in the products. My mobile phone battery dies in 6 hours, TV screen has pixel issue, soundbar doesn't work... What's going on?
Samsung support did a factory reset on my tv and it worked for a day and the issue came back.
Then a rep came out and went into the service menu and turned on and off the EDID option for port 3 (ARC) and then unplugged and replugged the HDMI cable. This fixed the issue and he said it was a common problem on the series 6 (2017) Tv's.
If you're TV is out of warranty then get into the service menu and switch EDID off and on. Otherwise get a rep to come out to do it for you.