I updated my T520 from NAE to NG1 using Odin and rerooted it with CF method and I was experiencing random reboots. I did tow things:
1. I defrosted the knox notifications in TB (I had disabaled it when super user asked me to...)
2. I went to SuperSU app's settings under cleanup I tapped reinstall and followed the given commands there...
I have not had a single reboot since then and it's been 2 days now...
I just wanted to share this with those that are having random reboots. Give it a try... It worked for me.