Shares of Slack (WORK) - Get Report  fell sharply after hours Wednesday even though the newly public messaging platform reported earnings that beat estimates and raised guidance. 

The stock was lately falling 14.67% to $26.35 a share, after having gained 8.03% in regular hours. 

Adjusted loss per share for the second quarter of the company's fiscal year 2020, its first as a public company, came in at 14 cents, narrower than Wall Street expectations of a loss of 19 cents. Revenue was $144.97 million, beating analysts expectations of $141.3 million. The revenue result was a 56.5% increase year-over-year. 

"This is an entirely new category of software enabling a once-in-a-generation shift in the way people work together," said Stewart Butterfield, Slack's founder and CEO, in a statement. "We believe channel-based collaboration is so superior to email-based communication for work, that this shift is inevitable." 

The stock was up 19% from its reference price in its June direct listing heading into earnings on Wednesday.

Management guided for adjusted loss per share for all of 2020 to come in between 40 cents and 42 cents, a slight improvement over its previous range of between 41 cents and 44 cents. Management expects revenue to be between $603 million and $610 million for the year, better than the previous expectations of a range of $590 million and $600 million. Free cash flow burn is expected to be between $100 million and $110 million for 2020, better than previous guidance of between $105 million and $120 million.

Slack CFO Allen Shim gave additional notes on the quarter in the company's press release. "Revenue growth was 58% year-over-year, despite a one-time revenue headwind from credits issued in the quarter related to service level disruption," Shim said. "We remain focused on expansion within existing customers and growing our large enterprise customer base, and ended the quarter with 720 Paid Customers greater than $100,000 in annual recurring revenue, which is up 75% year-over-year."

Nonetheless, investors seemed incredibly disappointed, and potentially finicky. "I imagine the reaction is picking on the deceleration from 67% year-over-year [revenue] growth in 1Q to [revenue] 58% growth in 2Q," D.A. Davidson & Co. analyst Rishi Jaluria told TheStreet via email. "I thought it was a solid quarter." Jaluria added that the revenue deceleration would have been more muted than it was if the $8.2 million in credits were stripped out of the equation. Excluding that item, revenue growth was 66%. 

"The only thing I can pick on is $100,000 plus adds were a little light, but $100,000 customers grew 75%," Jaluria said. Slack said it ended the second quarter with 720 customers paying annual recurring revenue of $100,000.