Essence monsters dropped no essences

As the title says I was in a T-4 Cemetry Map and killed a total of 3 essence monsters which none of them dropped their essences. I tried reloading, relogging and loot-filter option but there has been legit no essence droped. Even the Boss droped absolutley not a singe item, not even a white one. Is there a bug that cuases this?

Sincerly

Senghokai