UnityPlayer.dll crashes or hangs in standalone

I've got a problem with my game where after a few minutes (better or worse in certain areas) I get a crash:

UnityPlayer.dll caused an Access Violation (0xc0000005) in module UnityPlayer.dll at 0033:8fc9530c.
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In cases where I'm debugging the standalone, I'll get a hang with the callstack just spinning in a thread on waitforsingleobject with no useful information at all even after loading symbols.

Time seems to be key here, if I leave the game for a few minutes and return, it might crash almost immediately (when nothing is really happening in the game). My project seems relatively healthy if I look at the memory, no increasing GC objects or memory footprint during the times when it crashes.

It's super-intermittent so it's been difficult to pin down anything in the game that causes it. Since it crashes or hangs outside of my game I don't have any idea where even to start debugging this thing. I've been battling this for days and I need to demo my game in a week. Any ideas what might cause these sort of symptoms?

I'll attach the crash files in case it's useful:

 

I'll bump this since it's a new week and I still hold out hope that someone has run into this. Any thoughts?