when the TV turns on, I no longer have the CEC working.
Plenty of such CEC issues were already reported but solution has not been found yet. TV behaviour is probably a part of that problem.
I have the same issue with a Samsung TV, but this only started somewhere between version 8 & 9 of Kodi. There has also been a major libcec update in that timeframe. Some bisecting to find the cause might be possible. Do you have any idea what would be the most probably cause for the regression, Kodi or libcec (or something else)?