YouTube’s biggest stars saw their numbers plummet this year

YouTube stars with more than 10 million subscribers have experienced a sharp drop in viewership since February, according to a new study.

In the study commissioned by Kotaku, the social statistics tracker SocialBlade found that 49 big channels averaged almost 4.1 million views per day in January, but declined just over 3.7 million views per day by November. Most of the drop took place in the second half of the year. Those numbers exclude channels from major media, such as record labels and TV networks, focusing instead on “personalities” like Jacksepticeye and PewDiePie.

There’s some debate about whether the drop-off means fewer people are watching videos by YouTube personalities, or if YouTube is just counting views differently. One theory is that the decline is driven by YouTube’s intermittent purging of views generated by bots, although that might not explain such a long-term decline.

More intriguing is speculation that the moves are the result of changes in YouTube’s search and promotion algorithms that give less weight to subscriber numbers when evaluating individual videos. There has also been rampant speculation that YouTube is actively unsubscribing users from channels. YouTube has said it’s not doing this.

An increasingly heated war of words has been brewing between YouTube and a coterie of talking heads who found fame there. Some major stars have been willing to play devil’s advocate, though, arguing that making subscriptions a less important factor in YouTube’s algorithms could actually help the site’s overall health.

For more on YouTube’s strategy, watch Fortune’s video.

YouTube, for its part, has reacted by casting doubt on SocialBlade’s numbers, saying on Twitter that they “do not accurately reflect subscriber activity.”

Ouch ;( We don't make up data. We get it from the YouTube API. We rely on it for accuracy. If it has issues maybe ping them?

— Social Blade (@SocialBlade) December 20, 2016

This story originally appeared on Fortune.com. Copyright 2016