Not sure if this will help, but I removed test sd and reinstall orginal sd card and upon boot cec is working.
Still working 2 days later, seemed as it takes overnight till the two find each other and then works fine.
I had the same issue a few weeks ago with my Samsung TV after I added a new Cable STB. I lost all CEC data with all my devices, including my Rpi3. I came across an unofficial Samsung forum that explained that some of the chips that control CEC and HDMI are not as reliable as they should be, and need to be reset. The best way is to power down ALL your kit, everything, for about 15 minutes (I shutdown at the wall socket). This basically performs a reset on those components and gets rid of any residual “memory”. Then power everything back up, and it should work again. I have not had to repeat this. Please note that a 5 minute power down did NOT work. Give it 15 minutes.
P.S. My TV is a Samsung UN55HU7250FXZC. This never happened on my old Samsung Plasma.
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That could be correct, cause 3 days remote still working. I notice the tv seems to do some update / refreshing over night. Maybe refreshing of circuit happen when tv is powered off for period of time also. Just glad it is working again.
You saved my day !
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Glad it worked! 
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