Essences can fail to drop

Killed an essence enemy while in act 2 that didn't drop related essence.

Either essences can failed to drop randomly, or there is a bug where the essence won't drop if the corpse of that enemy is destroyed too quickly, I am currently wearing the Corpsewade unique boots that burst enemy corpses I walk over / near.

Not sure if the boots are related to the bug, but might be relevant info.