In a single row of 3 reviews in the Low Quality review queue today the third review would not let me select Delete, although the others would.
I didn't go below the Trusted User between those reviews, so I assumed this is caused by the "state" of the answer or the other reviews.
One of the other reviews had a "Looks OK" from another reviewer as well, so I assume that is not it.
This last review did have a positive score. Is that why I could only "Recommend deletion" and not "Delete"? Is that decrease of privileges documented somewhere in the help pages or somewhere else?
(Shortly after, @slm used his moderator powers to delete all 3 posts).