Sounds very familiar problem that I had as well around 2 weeks ago but managed to fix it. I made a post on us forums when I was looking the solution to fix the problem, you can check it here https://us.forums.blizzard.com/en/heroes/t/huge-frame-drops-and-1-sec-freeze/17217/11
Anyway, I got it fixed by updating my OS (Windows 10) MANUALLY, you can update your Windows 10 by going to Settings → Update & Security and then clicking the Check for Updates button. After that just update, it’s gonna take a while. That did the trick for me.
Decided to check if some people still have this problem, should’ve probably post this sooner here… hopefully this will fix your problem too!