The bug is easily reproduced.
Effigy of combustion 4/4 give you 100% chance Infernal Shade on Zombie Death TARGETTING ENEMIES.
But in combat it usually doesn’t create anything.
With Lingering Flame nodes (allow Infernal Shade to stay on the ground), we can see that it cast randomly on the ground and not targetting monsters even if it’s next to the Zombies.