Disabling CEC in system/input/peripherals/cec settings should avoid this (but will stop CEC remote control from working).
You may be able to disable some of the options there to avoid it.
I think really we want this libCEC included: use system audio mode request instead of power on to start AVR reliable by gdachs · Pull Request #208 · Pulse-Eight/libcec · GitHub
You would try a Milhouse nightly which does include that - does it work better for you?
LibreELEC Testbuilds for RaspberryPi (Kodi 17.0)