server crashing intermittant

Hi all I've been running a FTB and other Minecraft servers for sometime with no issues however I've recently built a Direwolf20 pack server and although its running it does from time to time crash I'm hoping somebody here might be able to help me as Im not able to see the problem

was running 1.012 recommended version but recent updated to 1.014 in an effort to fix the issue

the server is running linux ubuntu with 6gig ram on a quad cord cpu

attached are the error logs