I have a Yamaha sound bar that supports ARC. The sound bar turns off when I turn the TV off, and it did turn on a couple times but stopped. It still turns off but not on. I contacted Yamaha and got this response:
The HDMI control feature is automatically enabled once the HDMI input is selected on the soundbar.
There are no further settings or instructions to provide that are relative to the HDMI control feature on the soundbar.
You will need to contact your TV manufacture and inquire about the capabilities of the ARC feature.
Since the soundbar turns off with the TV remote control, the HDMI control feature is working.
Each manufacture has different functions pertaining to HDMI control.
I've reset the TV and sound bar and did a complete new set up a couple times and unpluged the tv for 5 minutes also. The firmware is up to date.
Samsung UN65NU800DFXZA 8 series
Lastly, I would recommend performing a factory reset on the TV. This will reset the TV back to the default settings. Let us know if this helps.