I’m currently finishing up a run of Chapter 2 of Dalaran Heist with the Druid. I am fighting against Zuramat the Obliterator, and got Frostmourne of my Lich King.
I used it alongside my hero power to kill of three of his major demons, only for nothing to happen. I definitely dealt the killing blow on all three, but nothing was summoned.
The last one was Malganis, if that may become relevant. I also had the double-use hero power. The run was in normal mode without any anomalies.
PS: I just noticed that there seems to be a lingering glitter effect on the play board. Not sure if this is related to Frostmourne.
Same thing happened to me. They all had the summon a 1/1 copy of itself deathrattle though… not sure if that makes them bugged out for a killing blow? I know that deathrattle anomly doesnt work right most of the time with other deathrattle effects. Wish blizzard would fix this game of all these bugs seeing as they are a mult billion dollar company… smh.