Intermittent in software may be quantifiable easily that way. Not so much in hardware. It may be temperature/humiditydependent. Perhaps a gamma ray flips a bit in the memory. All sorts of things that cannot be reproduced have probable scientific explanations. Except one of my clients, for they have angered the old ones who will be satisfied by nothing less than burning equipment. Either that or their ground is in adequate and the impulse tester randomly cooks equipment.