I'm on Xubuntu 14.04. When I originally upgraded, I had the problem of both light locker and xscreensaver running simultaneously. After that was fixed, light locker has been running smoothly.
But, recently, I noticed my screen on after I was gone all day; it was on when I woke up the next morning; etc.
I tried changing settings, rebooting, looking for other screensaver-like processes, checking that the command args would update when I made changes in the settings UI, etc.
I can manually lock the screen with
light-locker-command -l, but I don't remember to do that every time.
I wasn't able to find other askubuntu questions that address my situation.
Could there have been a problem with a recent update (I apply them appx. once/week)? Or, are there other things I should check?