I don’t know what it is, but I recently had these weird fps drops (ever since the Kanezaka update). My game fps dropped to 20 FPS making it unplayable and it felt like I was playing Cyberpunk 2077 instead of Overwatch. Sent multiple tickets to Blizzard support, but the replies did not seem to help. Was provided live support, where I downloaded the 357.09 Geforce drivers and doing a clean update. This ultimately fixed the fps drop problem. I then saw the Geforce Experience application deleted. Tried re-installing it to keep track of my graphic in different games. FPS drops came back, and in full effect. So I deleted it again, and it helped, SEVERELY. Then of course, I did the mistake of trying to install it again, which does lead to some fps drops, even now when I removed it, but only barely. Moral of the story: Do a clean update and install the previous driver of 357.09 and make sure the Geforce Experience application is deleted. Should fix all of your nasty fps drops.