Never played around with CEC so don‘t know if it will show anything, but turn on debug logs (menu/setup/system/logs/settings
Turn on, put them somewhere other than flash, worth ticking in extensions (press blue button brings up log manager) and then reboot.
..... and see if anything shows in the debug log (log manager, red button, select log and view).

ATV have a lot more code in the image for CEC (but doesn‘t mean it gives you anything more) which is why I wondered if you saw anything different.