New Realization: I had the lock cylinder removed when closing the door as I was diagnosing a problem where the door wouldn't lock.

(Apparently the car thought the door was perpetually open. Somehow that got resolved now.)

But when the door lock cylinder isn't in place, the carrier rides upwards by 1/8" or so. Maybe that prevented the door latch mechanism from "resetting."

Either way, I can't reproduce the problem now and I'm driving to Canada tomorrow, so hopefully there won't be any issues.