I can confirm trouble with HDMI eARC/ CEC on a 65" LG OLED65B9PLA.
I have the latest firmware updates, HDMI CEC permanently on.
Using with a Canton Smart Sounddeck 100 (2021, 2nd gen.), which receives also the latest firmware updates, supporting HMDI eARC, using a quality HDMI eARC cable to connect it with the TV eARC connector.
Both devices a instantly connected to the internet by an Ethernet cable. I tries several HDMI cables declared compatible with HDMI eARC.
The problem:
When I turn on the TV set the sounddeck doesn't turn on, or it turns on without sound or just with sound from the internal speakers, or it turns on with sound but setting the volume on the TV's remote is disabled.
I found out that most time, when I first turn on the sounddeck separately before turning on the TV the trouble does not appear. The same if I just put the sounddeck off and immediately on, the connection gets fully established.
I'd expect the TV waiting for the sounddeck coming up and connecting properly with all HDMI CEC options.
What I believe is the LG TV doesn't wait long for the sounddeck booting and answering the HDMI handshake and gives up the connection to early. Very probably a timeout from the LG side.
It takes some seconds for the sounddeck to boot when HDMI CEC gets active on the cable, altough it listens to it in standby mode.
Other sound sources to the sounddeck don't show this trouble, including Chromecast, DVD player, media player, etc. All they play fine when the sounddeck wakes up from sleeping and fully control it.
I've recently bought a LG OLED C9 PLA TV set, installed the latest version of firmware WebOS 4.71.XX. I like the WebOS interface, but there is one thing I absolutely don't understand and would appreciate to get solved: I use the single tuner in both modes, satellite and antenna. I'd like to have mixed favorites list from stations received from antenna and satellite and browsing between them without explicitly switching to satellite or antenna mode, thus having WebOS to automatically set satellite or antenna mode depending on the chosen station from the favorites list. At the moment this is quite difficult to handle: Open the list from RC, open the filter (yellow button), switch between antenna/satellite -> the list is reset to All, again choose the favorites list of my choice. I know it is possible to add mixed tuner mode stations to favorites, but there is always shown the portion matching the currently set tuner mode. This is quite difficult to handle. Isn't there another way?