Volcanic Fissure question

It feels like no matter how many fissures are on the ground, when activated by an aftershock, the enemy only takes damage from one fissure. Is this correct? if so, what's the point of the skill? I was expecting every fissure to add to the damage during the aftershock.

There's definitely something wrong with the skill. Even with that passive that makes you not miss, doing slam after slam on a fissure and the mobs health doesn't move on most hits. Please fix it ggg