So, this has been going around for a while now and for some reason Mojang hasn't picked up on it. When you play, doesn't matter what gamemode or perspective you're in, the screen will always suddenly become sluggish and unresponsive when you try to turn around fast. Many in our community refer to it as the 'sens glitch.' A vast amount of players are downgrading to 0.16.x or 0.15.x to evade this issue. Others are simply quitting because it affects gameplay so much. I think this sluggish sensitivity glitch is a byproduct glitch of the fixed 0.15.x and 0.16.x sensitivity glitch where the player looked up or down randomly, but this is just my theory. Anyhow, you'll be doing many people a favor by fixing this glitch. Thank you for reading this.
-Red and community
Edit: This hasn't been fixed as of the new update, 184.108.40.206.