If its intermittent it sound like a contact problem. With the Dereelight dropins the pill screws in to the reflector this can come loose. Mine does sometimes. Check that. What kind of tailcap do you have on your 6p? A Sf clicky or aftermarket. That would be the next culprit. I dont have alot of experience with SF clickies but some have had success with an alcohol rinse of the tailcap. If not you might have to ask SF for a warranty replacement on the tailcap. With intermittent operation it can make things more difficult to pinpoint.