I got a pretty tricky problem with my setup and I basically got no idea where the problem comes from. Setup:
TV: LG OLED 55 E6D (newest software version xx.95)
Audio Out (Optical/HDMI ARC)
Digital Sound Out: Auto
SIMPLINK (HDMI-CEC): On
HDR: HDMI 2 (ARC) turned on
Xbox One S (newest software version):
Audio Output Settings
Primary Output Port: HDMI OUT
Audio Format (Priority): Bit stream
Sound bar: SJ9 (newest software version)
Now to my problem. It seems like the paththrough is not working as indented. When I play a 4K movie the sound is played while the screen stays black or sometimes gray.
I bought the standard HDMI cable from Amazon (HDMI 2.0 a/b, 2.0, 1.4a - ULTRA HD, 4K, 3D, Full HD, ARC ....) and also tried the cable delivered with the Xbox One S (bought it 3 days ago). Both cables showed the same problem.
Now I tested another cable from a friend (HDMI Ultra HD Premium 4K, 2.0b 60 Herz) it turned out that it worked "better" with this cable, I finally could see the movie BUT when I turned it off and switched back to XBox the TV screen started to flicker also it did not automatically switch to HDR mode.
For me it clearly looks like that the 4k signal isn't rooted through the SJ9 in the correct way.
Sorry if something is not 100% clear due to my non native english