Item missing in inventory after bcnm

Platform: Windows
ISP: Free
Type of Internet Connection: ADLS
Internet Connection Speed: 1Mbps
Date & Time: Monday April 20th - 11:09 UTC+2
Frequency: Once (did not reproduce)
Character Name: Myasasa
Race: TaruF
World: Asura
Main Job: Thf, Lv.99
Support Job: Dance
Area and Coordinates: Walk of Echoes (P1) BCNM Lilith VE - Selbina
Party or Solo: Solo
NPC Name: None
Monster Name: Lady Lilith
Steps:
1. Entered the bcnm around 11:02 am UTC+2
2. Killed Lilith at 11:07:54
3. Log indicate "Malignance chapeau" and that i obtained it at 11:07:57
4. Zoned back in Selbina with the verdical conflux shard at 11:08:17
5. Check my inventory and there's no Malignance Chapeau
6. Called GM, discussed with GM Arestychy
7. After few minutes, he said that he couldn't find the item and that i have to post in the forum.