Monster with Essence suddenly dissapear

Was killing a monster with multiple essences, on t16 lava chamber map, monster is in the final boss room, already killed, and even spawn that essence golem monster, but no essence loot whatsoever

-already check my filter too, the boss seems suddenly just dissapear :/
-was playing CoC DD if that helps / give any clue

I had this too, i think it was some weird interaction if you use an allflame and one of these mobs spawned on map from the allflame converts into the essence mob, then they dont drop the essences