I've been using modern dynamo hubs for a dozen years, and old Sturmey Archer ones even longer. I've used a variety of lights, both home-made and factory made. I've experienced all kinds of weirdness. Usually because there's something wrong with the wiring. I'm not afraid of messing with electronics, but I have no subtle understanding of what I'm doing. I connect the wires, I try it out; if it doesn't work, I disconnect it and reconnect it and try again. Repeat until it works.

A few days ago I set up a Planet Bike Blaze Dynamo light with a new Shimano dynohub, a 6v 3w one, I don't remember the model number. Yesterday I rode to work in the dark, and it was fine. Good steady light while riding, steady but much dimmer standlight when I stopped. But today something has changed. When riding, the light flashes; a series of weak flashes, then one powerful flash, then no flash at all: so it's like

flash-flash-flash-FLASH-dark-flash-flash-flash-FLASH-dark-flash-flash-flash-FLASH-dark-flash-flash-flash-FLASH-dark

and it's really annoying.

And when I stop, the standlight function also flashes.

The light has a push button switch; it turns the light on or off. It does not appear to have multiple settings. Playing with the switch did not change the way the light was flashing.

Anyone have a theory what's going on, and how I can fix it?