I too am not getting Light Flow to work correctly. I just recently upgraded from the Lite version, but since I have installed the Pro version, no LED notifications are working (or at the most are working very sporadically). I have 4.1.2 installed, all stock, no root or modifications. It's not crashing, just not working very well at the moment.
I am running it on a GS3 though, so that may have something to do with my luck with it...