Usually when a release build crashes it means there was a bug in your code that just happened to never cause any visible side-effects in the debug build.
Usually it’s an uninitialised variable, or a timing-related race condition that only goes wrong when things run at a different speed. As for tracking it down, sorry, that’s a tough one. I’d normally start by disabling bits of code to try to close-in on where it might be coming from.