What time controls were you looking at? I'm half-jokingly wondering if the big dip of correct moves in the upper 2800 range is Nakamura's crazy opening style :) (He's rated upper 2800's in blitz and rapid)
My guess: the only one that has been rated in that bucket in the last year was Caruana, post-Saint Louis. At that point, he suffered (and is still going through) a big decline with several bad blunders.
This was the leading hypothesis on r/chess. I'm pretty sure it's right Naka didn't hit this rating in 2014 as far as I know.
The only other candidate would be Carlsen when he dipped to the high 2850s.