Epic Systems, the giant medical records software vendor, created an app store two years ago so that companies including Apple, Oscar Health and other providers of health apps could sync their services with patient data from large hospitals and clinics.

The Store, called App Orchard, became the major way for dozens of developers of health software to reach patients who visited some of the largest medical centers like Mayo Clinic, Cleveland Clinic and Massachusetts General Hospital, as well as the doctors that work there.

But in December, Epic froze enrollment in App Orchard, according to three people familiar with matter who asked not to be named because of the sensitivity of the issue. In an email to CNBC, Epic confirmed the move and indicated that it was temporary and related to security and privacy concerns with some third-party developers.

"Over the last few months we updated our App Orchard policies to help assure that apps operate in ways that keep patient data safe, private, and secure," an Epic spokesperson said in the statement. "During that time, the App Orchard remained open, registrations were received, but new enrollments had to wait until our policies were completed. New applications are currently being reviewed and approved."