Hello,
During a echo “necropolis streets” at the Spirits of Fire timeline, level 90, i encountered monsters named “concealed toxic sludge” and “concealed sludge” that on death, they applied multiple stacks of poison. As a melee (warpath void knight), i immediately got max stacks as i was in melee range and they exploded immediately upon death. The poison tick damage, even with max poison resistance (80% at time of incident) was insane and could barely survive it.
If possible please check the damage modifiers on that, or perhaps they can explode after 1,5-2 seconds of their death-just a suggestion 
Sincere regards,
Draconis