Evil Incarnate achievement Didn't Properly Complete

I specifically killed all 4 Survivors with double iridescent on The Shape and the achievement hasn't popped up. Is there currently a bug with this? I have a screenshot to show that I did, and I'm glad to verify in any way to try to figure it out.

Any help would be great, as it would suck to just have it yoinked from under me. :(

UPDATE: I did it again, and still haven't gotten the achievement on Steam.

Strange, I'm able to do the thing I've thought was impossible to do twice and the achievement isn't showin', kinda painful.

Edit: Grumble was the one I was talkin' to in the second ss. He asked if it was something to do with perks, I guess it's worth bringing up in case it leads somewhere. I have no idea why it don't worky.