Rengar 6.22 Bonetooth Necklace Vanishing! [GAMEPLAY]

I was really fed as Reng this one game, got the 5 unique champion kills early into the game, and got the head of Kha'Zix (giving me huge AD), and all of the sudden I noticed that my AD went from 670 to 370. I was confused, then realised my Bonetooth Necklace had completely disappeared from the UI and apparently from the game.

http://imgur.com/a/ZHEde (image of in game UI)