Hi!
In the couple last alpha releases I noticed some issues with screensaver activation... Finally I discovered that if I plug in my USB bluetooth device into my RPi2, the system does not enter in screensaver state, it is active everytime. I see the dongle's red led blinking everytime eventhough I disable bluetooth service from libreelec config tool...
If I unplug the usb dongle, then the screensaver works great.