I was guessing that these artifacts are a result of excessive clarity, but I just tried replicating it with several of my own night photos and couldn't replicate it. So perhaps it is a combination of substantial lifting of the shadows (which will often reveal problems, particularly at high ISO and if exposed to the left) with a boost in clarity (which would exacerbate them).
If the original histogram is bunched to the left, that might be a clue.