+1, sounds like a shaky contact. The switch ring is the first thing to check. See the tailcap where there is a ring with two holes in it? Tighten that firmly, you should be set.
Well tightened with special pliers has the things that stick into the holes so i had the right tool nothing yet cleaned threads too. Where do u send lights back to china?
No don't do that (yet)! Not only dumping the problem off on someone else or disclosing it for a loss, but also since it sounds like his is still new, send it back to the retailer for a new properly functioning one. Or back to fenix to get yours fixed if no longer within the return period, & if these guys' suggestions don't work for you. Try everything first obviously. Good luck!