Kuo is well-known for accurate reporting on Apple's supply chain. His note, reported by 9to5Mac, suggests that the shortage of units is related to several components used in the iPhone X. Originally, reports suggested the new 3-D face-scanning sensor was to blame, but Kuo added that the circuit board for a new camera is also causing setbacks.
Apple didn't disclose how many iPhone 8 units it sold during opening weekend, but the last time it did — after the iPhone 6s launch in September 2015 — Apple said it sold a record-breaking 13 million iPhone 6s and iPhone 6s Plus smartphones.
Given the hype around the iPhone X, one can see how having just 2 million to 3 million units may quickly lead to long shipment times. Kuo said Apple will likely fix the kinks in its supply chain by November, so it's still possible Apple is able to ramp up production ahead of the holiday shopping season.
An Apple spokesperson was not immediately available to comment.