I was looking at this question, and noticed that the OP's name in the comments is inconsistent (the style of the name, not the name itself).
OP has two comments on the top answer which are displayed normally, but also has a comment on both the question and the second answer which are simply black, unclickable text with no background color.
I've checked their profile; it hasn't been deleted or anything. I've also checked in Chrome and Firefox and the behavior is the same on both.
Any idea why this might be happening?
(This might be a question for Stack Exchange in general, but I've only seen it on this question, so I'm bringing it here first).