Twitter Inc. shares were tanking in premarket trading Thursday after bugs in the company’s advertising platform led to misses across the board on its financial metrics, even as user growth proved more rapid than expected.

The stock was off nearly 20% premarket as Twitter TWTR, -17.18%  said it was working to solve issues with its advertising platform that impacted targeting, measurement, and personalization capabilities but that it expected a further impact in the fourth quarter as well.

See more: Twitter stock plummets after earnings miss trumps user-growth beat

The company posted net income of $37 million, or 5 cents a share, for its third quarter. After adjusting for stock-based compensation and other expenses, earnings per share slipped to 17 cents from 21 cents a year earlier and came in shy of the FactSet consensus, which was modeling 20 cents in adjusted EPS.

Revenue climbed to $824 million from $758 million, but analysts were expecting $874 million. Twitter disclosed that it discovered some bugs during the third quarter that impacted the company’s ability to target ads and help marketers measure the effectiveness of their campaigns. Twitter “took steps to remediate” these issues, which it said helped lead to the disappointing revenue performance. Twitter also pointed to a lighter summer slate of events.

The ad-platform challenges are expected to persist in the fourth quarter as Twitter delivered a lower-than-anticipated forecast for the period. Twitter is calling for $940 million to $1.01 billion in fourth-quarter revenue and expects that the advertising issues “will likely result in 4 or more points of reduced year-over-year growth for total revenue in Q4, up from 3 or more points of impact in the third quarter.” Management is projecting a full-quarter impact in the fourth quarter compared with only a partial impact in the third quarter.

The lone bright spot in Twitter’s report was its growth in monetizable daily active users (mDAUs), reflecting product improvements meant to make notifications and timeline content more relevant. Twitter had 145 million mDAUs in the quarter, up from 139 million in the June quarter, whereas analysts were expecting 142 million.

Twitter shares have gained 35% so far this year, as the S&P 500 SPX, +0.00%  has risen 20%.