Mao Kun Essence Drop Bug?

Unfortunately didnt recorded a movie but... Killed all on Mao Kun (without essence weilder), talked to Fairgraves (who kills all remaining monsters) then approached back to essence and there was no monster and no essence on ground. After i "unfreeze it" just simple nova effect but nothing there. Did i lose essence? :(

I had the same problem, I've ran two different Mao Kuns and each time we opened the essence, nothing came out. I'm only upset because one was Essence of Delirium and I need it for a challenge :c