I started experiencing the same issues at the same time so many of us keep describing.
Technically-speaking it’s related to lower than normal FPS and higher than normal ping or packet-loss (widespread server-related issues), but visually-speaking it’s a sporadic microstutter/hitch that is most blatantly noticed when trying to aim and shoot consecutively while strafing in high-intensity battles and makes matches unplayable. One time it even caused my “rendering device [to be] lost” and crashed the whole game.
I’ve never had to deal with this before and haven’t changed any settings in-game or on my high-end PC. Only thing that could have changed is something on Blizzard’s side, approximately a week ago transitioning from the Anniversary event.
Yes, perhaps this is a separate and coincidental issue, but generally speaking–the game has not performed well and struggled with performance issues across the board in the last week or so for many more users than normally would complain.
Whether it is in conjunction with the post-Anniversary event patch, graphic card driver updates, or Windows updates all occurring around similar times I cannot say for sure, but something is certainly up!
Just remember the key to resolving it (or finding faults with the game software itself) is troubleshooting. Right now the game performs fine for a high majority of users. If you need help, try to post more details to things you have tried to stop the errors or poor performance (or share a DxDiag so we can learn more about your specific computer). Here are other important guides to go over as well:
I’ve got my MSInfo and dxdiag if you want it. I just logged in and played a Mystery Heroes match. Happened consistently from beginning to end of the match with 30 second intervals.