I think you missed a part.

Lights like the Convoy 2 ( + ) have three parts: the head, the tube and a tailpiece.

The A6 consists of four major parts:

- the bezel: here you find the lens, an O-ring, and the reflector,

- the “pill”: on one side you’ll find the PCB + led, and at the other side the driver + spring, and a retaining ring,

- the tube: a piece of aluminum pipe with threads and O-rings on both sides,

  • the tailpiece: with a PCB + spring + switch, a retaining ring, a washer and a rubber tailcap.

1/ MRsDNF has asked you to reverse just the tube. The manufacturer of the A6 does not use oversized pieces of metal. Sometimes two connecting parts just barely make contact, or barely not. Cleaning the rims of the tube and reversing it may help.
2/ Have you tried if the retaining rings on the driver and on the switch are properly fastened?
3/ You can test if the trouble is in the tailpiece by removing that part and short circuiting the (bare) backside rim of the tube with the underside of the battery with a pair of pliers or scissors.