On fleamarket found electronic flashlights (solo or in-camera) I repeatedly found samples that flash but nevertheless show no glow ("loaded" sign) at their indicator neon lamp. And I waited for some minutes to exclude cases were the circuit permits flashing before the break-through current of the lamp is reached.

Typically these types of lamps go for many thousands of hours.

Any ideas about the cause of such failures aside of a broken connection?
(Another cause might be a too high current through the lamp, and thus destroying it. Though I got no idea how such a current could arise.)