Are there any EEs on HN who can explain a characteristic failure mode of LED lamps---as well as LED-lit commercial signs---that very bright, metronomic 2--5 Hz

Are there any EEs on HN who can explain a characteristic failure mode of LED lamps---as well as LED-lit commercial signs---that very bright, metronomic 2--5 Hz flashing that they do? I've seen it happen to street lamps, desk lamps, commercial signage, traffic signals...it's not the usual 50 or 60 Hz flicker, but a distinct failure mode, regularly flashing a few times a second, like a circuit breaker resetting, but faster. It's distinctive to LEDs, must be something in the power supply. But why do so many LED lamps do it?