Hhmm, could be a faulty driver board or part - may get some cross coupling of signals with some intermittent contact or proximity interference - unfortunately still a few possibilities remaining...
Probably did this already, but go over the board carefully with a strong magnifier (microscope preferred) and check for nasty solder splashes or contaminants, or anything that looks too close for comfort. I always give drivers I build a close inspection and bath in fair amt of isopropyl alcohol to get rid of contanimants as much as I can. For me at my age, I need magnification and light on the object - equally important.
For the threads issue, interesting because the threads on the tail, for example, are anodized and don't conduct electricity - you have to look at where the electrical paths are, and yes, they can get dirty or have oxidation issues.
Thanks for your advice, Tom E and USA! So you would say that there is basically not a driver component responsible for flickering, right? I will try to clean the threads on the tail and the pill of the flashlight. If cleaning the driver does not resolve the issue I will try to swap another driver in the flashlight.
If you give it a cleaning, use a stiff brush with the isop. alcohol - I'm using a brush that came with a razor, maybe a toothbrush would do as well, or something similar - 90% isop. is good to use, nothing lower, available at most drug stores.
I’ve found flickering issues are very commonly associated with ground problems. The retaining ring on the switch pcb, or even the bare metal under the switch pcb, quite commonly causes these kinds of issues. Most likely there is a place in the multiple contacts that has dirt on it, visible or otherwise.
Richard has been using a thinner PCB for his drivers, make sure the driver is actually getting a solid contact on the retaining ring. If not, build it up some with solder blobs in a few places around the ground ring then double check the retaining ring.
That’s been pretty much my experiences too.
This problem seems to magnify drastically when you start pulling 10 amps or more, which Dale does quite frequently.
When asking for lots of power, connections, wire size and length, spring resistance and battery sag mean everything.