Legacy of the Vaal Quest - Stone Altar not Working

After retrieving the Large Soul Core i activated the Stone Altar to open the Matlan Waterways. It used my Quest Item and nothing happened.

I can still interact with the Stone Altar placing the Souls Core over and over again but the Waterways won't open.

I've tried killing the Boss again but he doesn't drop the Soul Core anymore and now i'm stuck.

EDIT: I fixed it by getting someone on the same quest state and let them activate it for me

the same with me