Chaos Theory - No More Mr. Fungi achievement

Has anyone gotten this? The hallucinations no longer spawn once your past this step. I tried it on another character that hadn't done the story and they de-spawned so quickly it was impossible to land a hit on a single one. Is this bugged or is there something I'm missing?

Thanks.

EDIT: lol...I figured it out.

how did you managed it?

Well, I think that what I was seeing the first time where the hallucinations appear for only a split second is somebody else's trigger of the hallucinations. After I actually collect the sample then the hallucinations stick around for plenty of time to kill them. Although I did have to do it on a character that had not already gone past that step. Hope that helps.

For those trying to do this as a repeat, it only works when your current story is active.