$3.8 billion Slack just lost another high-profile executive

Slack's head of product Jason Shellen has suddenly left the company, less than a year after joining the $3.8 billion startup, Recode's Kara Swisher reported Thursday.

It's unclear why Shellen is leaving or where he's headed. While his LinkedIn profile says he's still at Slack, the company confirmed with Business Insider that Shellen has indeed left.

"We can confirm that Jason has left Slack," a Slack spokesperson said. "He wound down his time at the company in late December to pursue a path closer to his entrepreneurial roots."

As head of product, Shellen was largely in charge of Slack's platform business, the company's effort to make its messaging app a broader workplace service that takes care of things like expense reports or meeting notes. Slack recently launched an $80 million fund to support this initiative.

Shellen's departure is the second high-profile executive loss for Slack in recent months. In November, its chief marketing officer/chief revenue officer, Bill Macaitis, left, leaving a huge position empty for the fast-growing startup.

The departures come at a tough time for Slack. The company is battling two new big-name competitors, with Facebook's new Workplace service and Microsoft's Teams products both aiming to scoop up the business users that have flocked to Slack's messaging platform.

For what it's worth, Shellen has a history of short stints throughout his career. In his previous position at Pinterest, he only lasted 10 months, while he only worked 10 months at his job before that, according to his LinkedIn profile.

Despite these changes, Slack has been adding firepower to its sales side. After hiring its first sales chief Robert Frati earlier this year, Slack also poached Dropbox's Kevin Egan in November.