Unchecked the box before I entered the Caldera of Souls, still after defeating the three bosses, the Harbinger of Ash spawned. Tried that severeal times, happened every time.
and on top of that, I noticde that Glyphs of Envy sometimes don’t get added to the right difficulty of the Mono: Did a lvl 90 Echo, used an Envy directly after and got stability added to the lvl 100 difficulty version instead the recently played 90.