poe 1 - essence monster do not drop essence

LOL...
I have a 3 Imprisoned essence monsters on a map.
The first one granted me essences, but the other 2 monsters just died and drops nothing.

Can't proof it because the Screenshot shows nothing useful, but here it is
(only essences from the first imprissoned monster in my invemtory, and other group of monsters are laying down nearby with nothing)


League: Necro Settlers