Snapchat packed on more daily users than expected in the third quarter of 2021, adding 13 million in the period to reach an average of 306 million.

But Snap’s stock was down 22% in after-hours trading — and plunged as much as 30% — after the company missed Q3 revenue expectations and CEO Evan Spiegel called out “significant headwinds” including Apple’s iOS privacy changes that put a damper on ad revenue.

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Snap reported revenue of $1.07 billion, up 57%, and adjusted earnings per share of 17 cents. That narrowly missed analysts’ average expectations of $1.1 billion in revenue, while the company topped Wall Street’s forecast of adjusted EPS of 8 cents. The company’s net loss narrowed to -$72 million in Q3 2021 (versus -$200 million in the year-ago period).

For Q4, Snap expects a revenue slowdown: The company forecast net sales of between $1.165 billion and $1.205 billion, or year-over-year growth of 28%-32% (lower than prior Wall Street estimates). Snap estimates DAUs will be 316 million-318 million.

In prepared remarks, Spiegel said Snap’s advertising business “was disrupted by changes to iOS ad tracking that were broadly rolled out by Apple in June and July. While we anticipated some degree of business disruption, the new Apple-provided measurement solution did not scale as we had expected, making it more difficult for our advertising partners to measure and manage their ad campaigns for iOS.”

Apple’s iOS 14.5 update now requires double opt-in from users to allow ad tracking. CFO Derek Andersen said on the earnings call that it’s still unclear “what the longer term impact of the iOS platform changes may be, and this may not be clear until at least several months or more after the ecosystem stabilizes and advertisers are able to fully implement the new solutions we are developing.”

Snap’s acknowledgement that it underestimated the impact of iOS opt-in ad tracking fueled concerns for investors in other internet companies, with after-hours trading declines for Facebook (-4.7%), Google (-2.3%) and Twitter (-3.4%).

Even with the iPhone privacy change, it was Snap’s first quarter of reaping more than $1 billion in revenue. The DAU count of 306 million for Q3 was up 23% year-over-year, as the social messaging and media company continued to show strong growth globally.

“We’re now operating at the scale necessary to navigate significant headwinds, including changes to the iOS platform that impact the way advertising is targeted, measured, and optimized, as well as global supply chain issues and labor shortages impacting our partners,” Spiegel said in announcing the results.

Meanwhile, submissions to Snapchat Spotlight, the company’s user-generated content section patterned after TikTok, more than doubled over the prior quarter (but Snap didn’t disclose figures). After doling out $1 million daily to top Spotlight creators, Snap in June reduced the amount it pays overall because the program was generating too much “copycat content,” Spiegel said an investment conference last month. In early October, Snap launched Spotlight Challenges in the U.S., which promises cash payouts of $25,000 or more to creators with the most-engaging videos that use specified AR lenses, sounds or topics.

“We will continue to build Spotlight into a unique entertainment destination for our community and a rewarding creative outlet for people expressing themselves through our camera,” Spiegel said.

Media and entertainment partners “continue to find success on our platform,” Spiegel said, with 15 different partners each reaching over 50 million Snapchat users in Q3. He called out two of Snap’s originals that launched in the quarter — reality series “Meme Mom” following creator and new mom Nicole TV (Kayla Nicole Jones) and “Honestly Loren” starring digital influencer Loren Gray — which each reached more than 10 million viewers.

Snap ended Q3 with 5,190 employees (including part-timers and contractors), up 40% annually. The company’s stock-based compensation expenses in the quarter were $300.9 million, up 57% year over year.