The decline put the stock in negative territory for the year, down 23% compared to a 3% increase in the broader market.
Shares slumped following the online health insurance provider's second-quarter report -- even though that announcement showed strong sales growth and a near doubling of adjusted profits.
Investors looked past those encouraging headline results to focus instead on a potentially worrying uptick in customer cancellations. CEO Scott Flanders said in a conference call that executives have a "comprehensive action plan" aimed at addressing the issue.
The big concern is that rising cancellations indicate a shaky market share position, or other challenges with eHealth's customer acquisition strategy. On the other hand, management boosted its outlook for the rest of 2020, suggesting the retention problem may be more of a short-term issue.
Investors will have to wait until the healthcare company's next earnings report, in late October, to get clarity on whether eHealth has a potential growth challenge on its hands.