User blog comment:Ghmorello/Chappter 883: My, What Big Dogteeth You Have!/@comment-24850639-20171027153711/@comment-3387274-20171027162534

Luffy's found a circumstance under which Observation Haki can't see things coming, by the looks of it. I think it might be connected to how Katakuri surpassed armament haki, but that wouldn't be much of an advantage since as long as Katakuri stayed calm he still controls the fight that way, so perhaps not.

Now that I think about it, the Admirals logia transformations even when exposed to haki might have been something similar, although that could just as easily be dodging things.