Essences in map don't give essences after defeating the main rare mob

i'm mapping in a T16 Strand map and i did already 3 essences. Clicked on the monolith to make them spawn, cleared all the mobs with the main rare one and it didnt drop any essence. But the normal loot still drops as i got a six socket armor piece from one of the main rares but just no essence (double chcked my loot filter and pressed Alt but still nothing).

file:///C:/Users/yannb/Pictures/Screenshots/Capture%20d’écran%20(76).png

this is the image, as always i hope you can have acces to it (otherwise bug report number is 3 504 045 770)

I concur this happened to me in a map. Essences dropped from the first two or three monoliths and then stopped dropping for the remaining monoliths. I don't have more informations to provide sadly