[Feast of Souls] as a hero talent gives you a chance when you kill an enemy to grant you 1 succulent soul guaranteed and 1 soul shard.
[Quietus] is another talent in the hero tree which allows a proc-chance to happen whenever you cast a Demonbolt, this means whenever you cast a Demonbolt, you have a proc-chance for this Demonbolt to generate 3 Soulshards and 1 guarantee Succulent soul.
The Bug happens when, associated with [Spiteful Reconstitution] - Bug: sometimes this Guaranteed Succulent Soul is consumed by the invisible 1-shard Hand of Guldan that [Spiteful Reconstitution] trigger to summon its 1 wild imp, consuming the guaranteed succulent soul and denying you from using it on a better 3-shard consuming Hand of Guldan.
In short [Spiteful Reconstitution] consumes your succulent soul.
How to Replicate it: Cast Demonic-Core consuming Demonbolts at 0 soulshards as Soul Harvester Demonology Warlock, you will notice that when Feast of Souls procs you will generate 3-soulshards (instead of 2) and at least 1 Succulent Soul but sometimes you will generate 0 Succulent souls…