The iPhone 5S’s long-rumored fingerprint sensor is still apparently proving difficult to mass produce. Digitimes reports that Apple’s supply chain partners are still having major problems producing the next iPhone’s fingerprint scanner on a wide scale and that low yields of the sensor could cut iPhone 5S shipments in the third quarter from an expected 10 million to as little as 3 million. Low supplies of new Apple products are nothing new, of course, as last year both the iPad mini and iPhone 5 similarly faced production woes that limited their early supplies when they first hit the market.