Essence bug (monsters don't drop loot, they just disappear)

I'm farming Essences in a Strand Tier 6 map, and I’ve run into a very annoying bug.
Sometimes I kill the Calcified enemies and they don’t drop the Essences.

It doesn’t happen every time, and not even in every map. I don’t know exactly what to do to reproduce the bug, since I’m not sure if it's caused by a combination of Essences, map modifiers, or something else. Even within the same map, it happens with some monsters and not with others.

I'm using all the Essence nodes on the Atlas Tree except Crystal Resonance.
On the Map Device I'm using Essence for 4 Chaos.
And I'm running the following Scarabs:

Adversaries

Calcification

Adaptation

Stability