Mastodon Tusk is not dropping

On my second Char the Mastodon Tusk doesnt drop even after doing the Boss 5 Times and resetting the Map it just doesnt drop. It Tells me to go to the Bone Pit and than to recieve the Tusk and I think normaly it would tell me to find the Boss location and kill them for the Mastodon Tusk but that doesnt happen and it never drops. Any Idea how to fix that because I cant progress without the Item ^^

try complete this mission by coop, it was helped to many people

Same here it doesn't drop

i have found that if you are wearing the Devouring Diadem Wicked tiara the tusks dont drop i didnt have it drop twice and changed helms and it dropped for me