The logs don’t seem to include the crash. But it does have this:
Negativity loaded a new chunk [-1059, 1807] in dimension 0 (overworld) while populating chunk [-1058, 1807], causing cascading worldgen lag.
which is a fairly good indicator that part of your problem is lag caused by world generation. Players are discovering new chunks, which often triggers more chunks to be created (as above), and lots of that will chew up all your server resources.
A good solution is to set a world border, and use a plugin or mod to pre-generate all the land inside it. That can take a while, depending on how big you need it to be, but it means the server doesn’t have to do it all live.
Another thing I can recommend is using Aikar’s java start-up flags to manage the memory better (if you haven’t already done so). Garbage collection with 30GB can be scary if not managed well.