Just swapped from RPi3B+ to RPi4B and I have the same issues - Samsung TV and CEC not connecting.
Other issues include:
- When switching back to TV the HDMI and CEC grab focus back and switch back to Kodi while trying to reconnect ever 2min or so
- Press the buttons sometimes there is a click, 1min of nothing and then all clicks hit at once and Kodi crash
Ive tried all of the above myself, looks like its back to RPi3B+ for the time being.