Remove the tailcap and bypass the switch with a paper clip to find out if the switch is defective. If its not the switch, see of you can unscrew the bezel and remove the reflector. With reflector removed, inspect the wires, solder and traces attaching the wires to the emitter board (star, MCPCB) to make sure they weren’t damaged by the reflector during assembly. Sometimes, if it was screwed on too tightly, this can crush the wires and/or nylon spacer between the emitter and reflector, causing an intermittent short, and sometimes a dead short. This symptom can also dislodge the emitter from the star, causing intermittent contact. Pressing down firmly on the emitter with your thumb can uncover such a fault, requiring you to ether reflow the emitter back into the star, or replace with new. This is all very unlikely with Olight, but Ive been surprised more than once with quality name brand lights.
If those check out, its probably the driver.
Good luck!