UE4 4.12 packaged game randomly fails just after launch

I'm having a strange problem with the first packaged build of my game. It's randomly exiting a few seconds after being started with no useful information in UE4's log. Sometimes it works, sometimes not, with no real clue as to why. It always works running the editor's VR preview mode or running standalone in editor.

I've put the HMD enable node in a loop in the level blueprint's begin play event to make sure I get a successful enable before proceeding. There's a small delay in there and the infinite-loop count is high enough that it doesn't have time to trigger the infinite loop check before it exits.

Any clues for where to look in Oculus' logs or anything else I've forgotten would be much appreciated.