• E-commerce site comes back online after going down on Monday
  • Yogawear company has been working to improve performance

Lululemon Athletica Inc.’s website suffered a lengthy outage on Monday and Tuesday, dealing a blow to the yoga brand’s efforts to draw more online shoppers.

The company’s North American site crashed after a power failure and other problems at a server farm, according to a person familiar with the situation. The site is now back online after being down for less than 24 hours, said the person, who asked not to be identified because the details aren’t being shared publicly.

Laurent Vasilescu, a Macquarie analyst in New York, said he first…