Video freezes in Safari unless mouse moves but sound continues
This is one of the most annoying problems ever. Safari simply doesn't play videos smoothly unless mouse moves. I followed all the steps mentioned before (clear cache, delete files, history, cookies, etc...) but the issue is still there. Usually the problem disappears for a while if I do system reset but comes back later.
iMac with Retina 5K display, iOS 11.2.6, 27"