re: Intermittent problems are tough to fix
As an engineer of many years experience, what we would do is stress the intermittently failing unit. Extremes of voltage, temperature, and varying clock skew. Good for finding intermittent hardware problems but this would often be moot if it was a software "race condition". In such cases or in intractable HW cases nothing is better than making a wise series of "intuitive' hypothethes followed by experiment, to at the very least rule out some causes.