act 3 small core

Can not progress: Stone Altar not accepting small Soul Core
I am in Jaquan's Machinarium, I have Small Soul Core in my inventory. Each time I leave this zone the core drops to the ground so it must be a "use here" item. I have cleared the map entirely up to the door beyond the altar.

The Legacy of the Vaal quest tracker is instructing me to "Place the small Soul Core into the Stone Altar". When move my cursor over the stone Altar it lights up indicating that it can be interacted with. Clicking on it but nothing happens no error or animation.

i am having the same problem my character does the animation placing the stone in alter but passage to waterways does not open.
i do not have a soulcore in my inventory for some reason and when i re place the small cores and kill the boss again nothing drops. please help!