Other than that the watermarked image has a bit more jpeg compression, I can’t say I see any difference between the two.
Sorry for being rather un-helpful!
Having said that, a thought just struck me.
what I’m referring to is the different layers of color and lightness on the edges of the black. [emphasis mine]
What quality setting did you export at? What if you export as jpeg using a higher value? Does that help?
Sort of shooting in the dark here (pun intended),