Serious Bug: Chapter 2 key mission item "Mastodon Tusks" didn't drop!!!!

When doing the mission of "A Theft of Ivory",
After those 2 bosses are killed in "THE BONE PITS",
The key mission item "Mastodon Tusks" didn't drop!!!!

I played serval characters from the Start of EA launch,
This issue already appear more than 7 times.
Why this Serious Bug in the main campaign still not be found & fixed till now?

Please help to fix this issues...