Prior to Chrome 85, there was a bug in Cumulative Layout Shift on pages with video elements. Hovering over the video element so that the thumb slider was visible would result in layout shifts when it moved. The bug was fixed in Chrome 85. The source code of the change can be seen here.
This change only affects metrics for a very small amount of sites. Desktop sites with video elements that users hover their mouse over for an extended period of time will have lower CLS values starting in Chrome 85.
We do not see an impact from this change in our overall metrics, so we believe the effect on most sites will be minimal.
Most users were updated to Chrome 85 the week of August 24, 2020.