Do you have any other devices connected to the TV/AVR? And do CEC work for these devices after a standby cycle without explicitly searching for devices?
Please try the following:
- Use Milhouse's latest Testbuilds for RaspberryPi from LibreELEC Testbuilds for RaspberryPi (Kodi 17.0) (contains latest libcec)
- Make sure your Pi is the only HDMI-device connected to your TV to minimize CEC interference
- Enable debug logging and libCEC component logging in kodi
- Disable CEC setting for turning off/on TV or device in kodi
- Restart your Pi while your TV is on and the Pi is the current input
- Wait until kodi is fully started
- Put your TV in standby and power it back up a minute later
- After a minute, setup CEC like your described (Menu -> Search for devices -> Select Kodi)
- Post your kodi log
Above should help determine if there is any new vendor specific cec commands that needs to be implemented