Boss fights with multiple bosses sometimes don't drop anything

Not sure how to replicate or exactly what triggers this bug, my guess is it probably be related to DoT or poison, playing a poisonburst arrow/toxic growth build.

Maps like the Sealed Vault, where you fight more than one boss at the same time, sometimes killing one instakills the second, both bosses die at the same time - even though one of the bosses had more health than the other - and they don't drop loot.

EDIT: i figured out why both bosses are dying at the same time: it's most probably from bursting plague support. I don't have culling strike anywhere.