Can not enter Mine Encampment

Hey,
usually I do not play Delve but wanted to enter the Mine Encampment just for the sake of an easy Challenge completion.

First it was not on my map. I spoke with Niko and got in on my map now.
But when trying to enter it, game says: "You do not have the required quest state."

My current Quest related to Niko is to visit him in his Encampemnt, "Niko's Fuel".
I read that I need to find three Sulphite locations. I looked into the Mines in Act 4. Nothing there.
Also in my Maps I did not had a single encounter yet with him or Sulphite.

What do I miss?

The Sulphite should just be occasionally found in random maps; you interact with 3 of them and, each time, he appears and begins mining away. Immediately after clicking on them you can wander off and leave him behind; no further interaction is required.

Is it possible that your Atlas passive tree is blocking the mechanic?

Oh thank you. That worked. I used a Scarab for him.
No I did not yet skilled the Atlas tree to not contain it. It seems like I was just super unlucky in that regard.