Though the iPhone X – Apple’s special edition iPhone announced in September featuring facial recognition and no home button – isn’t due for release until November 3, reports of production woes are marring the run up to the launch. However, thanks to a Wall Street Journal Report, we now have a better understanding of what’s causing the trouble: a pair of components dubbed Romeo and Juliet.

The idea is these parts are what the WSJ calls the ‘yin and yang’ or the device’s facial-recognition system which unlocks the phone in place of the TouchID.

The problem is, the Romeo modules take longer to assemble than the Juliet modules, creating an imbalance in supply and a subsequent bottleneck in the device’s mass production.

Other reports have also noted that there may be yield issues surrounding some of the key components of the iPhone X. Some have noted that Apple’s manufacturers have only been able to create components that meet standards around 60 percent of the time. This means only around 10,000 devices are estimated to be completed each day – which math fans may note is far too low to be able to meet the demand of the millions of sales that are expected for the device.

It’s led some commentators to question whether some pre-orders will receive their devices until 2018.

The demand for the iPhone X has also led to reports that the iPhone 8 has performed poorly, but recent analysis indicates that sales are around half of that the iPhone 7 achieved last year which not only makes sense when many will be holding out for the X, but is also in line with Apple’s own expectations.