I've noticed similar issues with the past few week's nightly builds of v8.0. After a while, the device seems to go into a 'sleep' mode where the HDMI thinks it is off-line (just get a blue screen with a no-device error message on TV). As a result, the CEC is not functional. I have an IR remote and also a USB remote, both of these can 'wake the device up' and return to the Kodi display, but the CEC doesn't 'wake' the device. Once 'awake' the CEC is re-enabled and works fine. I'm currently running the 8.0 7.30.2016 nightly build (LibreELEC-RPi2.arm-8.0-Milhouse-20160730210516-%230730-g0bc2994), however I saw it on previous 8.0 builds too...just don't remember the version I had been running. Prior to that I had OpenElec running Kodi 16 and had no such issues on same hardware. Screen would dim, but still be alive.
BTW...have the screensaver set to Dim (not black screen), so not sure why the HDMI thinks it is going offline.
Other than this issue, I have not encountered any issues running v8.0, and I'm using NextPVR as backend...works flawlessly.
Forgot to mention, this is on a Pi3.