For my Samsung CEC problem with my pi3 I studied the Vero 2 problem from makk509 and used the following commands:
sudo systemctl stop mediacenter
sudo nano /usr/share/kodi/system/peripherals.xml
sudo nano /home/osmc/.kodi/userdata/peripheral_data/rpi_2708_1001.xml
sudo systemctl start mediacenter
in both xml’s I changed the device_type from 1 to 4
and in actual the CEC seems to function normally… TV turned On/Off/On with changing source and it does work…
I will observe and test the pi3 a little bit, but eventually this could be a solution. It’s worth a test for everyone with the same problem.