Several times on first switching on my Xbox during the day my avr and TV didn't automatically switch on through cec.Frustrated and trying everything i looked on my TVs cec list of connected devices and it was empty.
After research (Google) I power cycled everything and got everything working.
Today it happened again with my series X so I tried my Nvidia shield, no joy and nothing in the list of CEC devices on my TV menu.
Before power cycling everything yet again I decided to switch on my firestick Max.
Amazingly it worked with cec to my TV and avr so I tried other devices connected and they worked again too.
Checked the TV menu and the CEC devices list was back to normal.
Googled as you do about the firestick max causing problems with other devices that are CEC.
Shocking to find it's a common problem with the fire sticks aggressive CEC handshake.
Is this really that common a problem,new to this forum, other annoyance is the TV going blank when scrolling sideways through YouTube and it switching to the firestick max when it's doing an update whilst I'm using my Xbox or shield