If I recall correctly from the BLF thread, the clip does help it function correctly. There was a bunch of complaints with clip vs no clip and the tailcap glued vs no glue (how it is now)
You can try cleaning the contacts on the head's circuit board and the body tubes.I received my FW3A about two weeks ago and it has ruined me for all my other flashlights. Its size, output (with XP-Ls 5000K), and UI are all fantastic. It occasionally gets quirky (only flickering when attempting to turn it on) but a quick unscrewing and replacing the head fixes it (though does leave me a bit worried for its longevity; as I said it's only two weeks I've had it). I'd like to order a deep carry clip for it, but the only place that sells them are Neal's website, and his communication and shipping records are not the best.