did you get it wet perhaps?
or
maybe it was a made in china knock off imitation.

that is why i purchased mine (Fenix TK11 Black, R2 Edition) from a USA retailer
https://www.fenix-store.com/product_...roducts_id=650
they are actually a branch of https://www.4sevens.com/

this other shop... i do not trust, even though it claims to be USA
http://www.fenixtactical.com/fenix-tk11-r2.html