The workaround is to stop using HDMI CEC 
The major issue is there's almost NO compatibility between HDMI CEC capable devices, every vendor supports a different subset of HDMI CEC features and often it's a nightmare (or it's even impossible) to make it working as you wish.
This is my experience based on long-time experimenting with 2 TV sets & LibreELEC's HDMI CEC support. Then I gave it up completely.
So the question is what do you need from HDMI CEC.
In my case it was just to turn on / off the TV set/display per request from LibreELEC. Even this most simple request did not work on my old LG TV as it was not possible to turn it off through HDMI CEC (the command was accepted but ignored).
In your case TV accepts power off command but then stops receiving further HDMI CEC commands until turned on manually again. Perhaps there is a sleep command that you can use instead of power off. Also check if your TV does not offer some more deep HDMI CEC configuration.
As I am using RPi 4B devices, the solution was to use GPIO pins for:
1) control a relay for powering the TV/display
2) send IR commands to TV
A simple additional hardware (a relay, some resistors & transistors and IR diode) is necessary but it works much more universal and 100% reliable.
