Quest item disappeared

Item quest that drop from "Zalmarath, the Colossus" just disappeared from my inventory.
I try to reload and kill the boss again for a few time but no drop.
please elp. <3

Character detail
name: Guillermore
level: 25
Class: Witch hunter
Steam id: todance

Check Zarka at caravan, good chances you gave it to her.
If you completed all 3 areas and miss the horn the should be an option to take the reward (horn of the vastiri).
If you didnt complete the 3 areas to recreate the horn of the vastiri do the missing ones and talk to her at the end.