Game crashes at random

The game I've been working on crashes when played for ~20 minutes (out of editor) for no apparent reason. I'm using ProBuilder (a LOT), DOTween, and creating and deleting a lot of things at runtime and running a lot of things in update. Objects that fall out of the world are never destroyed (yet?) until a new level loads, but that doesn't seem to be a direct cause of the crashes.
I imagine any one of these things, or all of them are contributing to eventual crashes, but I really don't know where to start in looking for where to solve this issue.

Any hints on HOW I can start looking for the cause of something like this?

 

Attach the profiler to your game's process in order to monitor performance and memory use.

http://docs.unity3d.com/Manual/ProfilerWindow.html

 

Thank you! It seems like running DOTween functions in update is a bad idea but I'll have to test if that's the cause of the crashes.