Description: Often the skill stops gaining souls and it's NOT due to the "Limit for same type of enemy still applies; maximum 20 from same target, maximum 1000 from same type of enemy" - I double checked that. I got 78 stacks of [Harvested Souls] in Chassizz then the skill stopped gaining souls anymore.
Since: 10.7.0.2000
P.S. There was a similar bug with the same skill in the previous version(s) of the game prior acquiring the level 60 elite skill [Psychic Homicide]. However, obtaining [Psychic Homicide] fixed the issue (or at least I couldn't reproduce it anymore). Did you copy that bugged implementation?
