CEC is a total cluster "you know what." Turn it off and make sure it stays off, and just turn your units on as you need them.
Sadly
@TLS Guy is correct. CEC is a mess, and in my opinion worse with Sony gear, as they've taken HDMI Handshaking to a new level of frustration and CEC along with it. I have two Sony receivers, a couple of their Blu-ray Players, and a 4K one as well => all on various HT systems (I have 4 of them. Yes I know I have a problem.) I have found that the sequence devices turn on affect operational success and many times lead to failure.
All you can do is try different configurations like plugging the Firestick into the TV and relying on eArc to get the signal to the receiver. By the way, it wouldn't hurt to check the HDMI Cables all work well and meet the specifications needed for all the devices connected.
But as suggested, you may have to just turn CEC off and live with pushing an extra button or two on a remote.
I know life is Tough!
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