Samsung soundbar HW-Q950T switches "arbitrary" between HDMI1 and HDMI2

[Arepa123]

Hi

I have a HW-Q950T soundbar where the HDMI out ARC is connected to my TV (LG OLED B6 - ARC input), and I have an Apple TV 4k connected on HDMI2 and a NVIDIA SHIELD TV connected to HDMI1.  When I turn on the Apple TV or Shield the soundbar switches back and forth between HDMI1 and HDMI2 repeatedly. After about 30 seconds I can manually select on of the two input without it switching back to the other. Any idea what is causing this? Are there any setting I can change to prevent this behavior? 

On other models of the Samsung soundbars you can manually turn on/off off CEC/Anynet+ by holding the right button on the remote for 5 seconds, this does not work on my model. Is there any other way to activate/deactivate CEC? 

I am running the latest FW: 1017.5

[MrEWhite]

I’m getting the same issue on my LG CX TV and my HW-Q900T soundbar, but instead of switching from HDMI 1 to 2, it switches from HDMI 2 (which my Shield Pro is on), to EARC and back again over and over. If it matters, I have a Panasonic UB820 4k Blu-ray player on HDMI 1.

[Arepa123]

I disconnected my Apple TV from HDMI2, and now I get the same symptoms as you MrEWhite, switches back and forth from Nvidia Shield TV on HDMI1 to the ARC connection.

Seems to me like the CEC protocol is not properly implemented on these Samsung soundbars. I had my Apple TV and Nvidia Shield and three other devices connected to an Onkyo receiver before, with the same LG B6 TV, and there CEC worked flawless with every device.

Hoping that a firmware upgrade will address this issue. 

[MrEWhite]

I found if you disable just the Auto Power Sync portion of CEC in the TV’s settings, it fixes this while allowing the rest of CEC to work fine. Not very convenient, but it works.

[Murphmrm]

I had that. eventually figured it's because I plugged my apple and cable directly into the sounbar along with the hdmi arc which also went to the TV. eventually I tried hdmi arc from soundbar to TV. then apple and cable to TV not soundar. ensured TV was set to hdmi arc. all seems fine now. FYI I also upgraded my hdmi cables

[MrEWhite]

I can’t hook the Shield nor the Blu-ray player to the TV as the LG CX doesn’t support DTS pass through.

[Murphmrm]

try shield in the sounbar and others into tv

[MrEWhite]

I tried that already, it still occurred. Again, turning off Auto Power Sync in the TV fixed it. Or, turning the soundbar on with IR controls in the Shield when waking the Shield also works (so the Shield and the soundbar turn off at the same time).

[Arepa123]

I have the same setup as MrEWhite, I want higher bitrate for the sound than regular 5.1, which is maximum you can get over ARC. So I need Apple TV and Shield TV connected directly in the soundbar to get for ex Dolby Atmos from both devices. Trying a bit back and forth I think it might be my LG TV that is not communicating correctly over CEC. Turning off CEC on the TV, it seems like the Samsung Soundbar, Apple TV and Shield TV is working as they should with changing input and power up/down. Which I guess is the same conclusion as MrEWhite.