Late response, but yes, the issues are persisting with the 8.0 release (at least for me). Sometimes CEC magically starts working immediately after using Kore to remote control Kodi, sometimes it takes a reboot, I haven't been able to spot a pattern there yet.
same here with RPi 1
I will try the hint from JimmySmith
Edit: I tried various setting but CEC is still not working reliable.
seems only solution at the moment is to use old firmware