My SON hub/Edelux headlight has functioned flawlessly since I built the wheel 3-1/2 years ago/maybe 3500 miles. There have been no accidents involving the front wheel. It worked fine on my Monday commute. Tuesday morning, it took about 100 meters to light up and was stroboscopic instead of a steady beam of light. It has always "flashed" at a walking speed but this was underway. I heard what sounded like freehub pawls in the front wheel for a few seconds. The light came on-went off-came on-went off. I stopped and checked the spade connectors between the generator and the light. I turned the Edelux on and off as I rode. The stobe frequency varied but it did not seem connected to my rate of travel. At some points it was "quick flashing" and at other points it cycled on and off at 1 second intervals.
The next morning it had slightly different failure modes-the headlight would go off but the stand light would stay on. There were times when everything worked as designed. At times it went completely dark.
I called the importer and he suggested I pull the wheel and skewer and try the bearings by hand-it appeared as it did when new.
The 3rd morning it was acting up and cycling at aboujt 8-10 second intervals. It was off at one point and I slowed for a stop sign-the light came on. I didn't think anything about it but a few seconds later, again with no light, I slowed for traffic and the light came back on. I tested this reaction both by coasting to slower speeds and by brakiing while the light was dark. The light came on each time as I slowed to about 6(?)mph, and functioned fine for a few moments. For he last 3-4 miles of the commute, it worked as it should-full beam, all the time. Today was the 4th day and it was fine - no failures, no strobing.
I have this set up on 3 bikes and have had no issues of any kind over several years of vigorous use.
Thoughts?

I have Shimano and Sturmey dynohubs with a B&M light and have occasional seen odd behaviour. Generally it is the connectors but once I had to cycle the lamp switch a few times. The generating part of the hub is pretty simple and not likely to go bad. I'd be inclined to think your first check should be for a small break in your wiring. Perhaps the sound you heard was the wiring hitting rotating spokes.

Good point. It was dark.... I'll check into it.

If your light system consists of a generator and a back up battery or capacitor, then the problem may be in the circuit that regulates voltage and switches back between the two. Or it could be in the backup unit itself.

If all is good, it shouldn't flash at low speed (except maybe when first starting out with a capacitor), because the back up device should be engaged and provide a steady current.

I'd put a voltmeter across it and see what's happening at various speeds, and see if that gives you any clues.