When fighting Helya in Maw of Souls, there is a very high chance that adds spawned in phase 2 by the Dusk affix will evade bug. There isn’t really any rhyme or reason for this, as I spawned them both on top of and off of the holes that tentacles make in the floor and it happened sometimes in both situations.
What’s worse about this is that when they do evade, they won’t snap properly to their aggro target; instead, if you get too far away, they will snap you to their location and if they are on top of a hole then you’ll also eat the damage and stun from being pulled into that.