In a thread quite some time ago I made the following statement: "AdSense doesn't allow autoplay video ads!".... boy was I wrong...
So I discovered that my site was plastered with autoplay video ads by some obnoxious youtube channel. Just spent an hour or so manually filtering them out. Just go into your Ad Review Center, filter by Ads Matching "youtube" and select rich media and see for yourself.
In the impression reports I saw that these ads always appeared before a significant drop in CPC, which might indicate that there might be some sort of quality score that is based on your historical performance (or the day before).
Be careful people.