

Even before this drop in views, the rule was you have to watch a video for at least 30 seconds before it counts as a view, as a way to combat clickbait where people instantly bounce from a video. Maybe they have changed this further? Or they change some kind of bot detection?
It could even be something “innocent” about how ad-blockers have started to interact with the site as YouTube ramps up their anti-adblock measures and the ad-blockers have to change how they work. Like maybe the ad-blockers have started blocking the JavaScript callback that logs the views.