It's not just consumer demand that's constraining supplies of Apple Watch. The Wall Street Journal is reporting that Apple has discovered a major defect with the watch's taptic engine, which is what causes the device to vibrate or "tap" users whenever they receive notifications and alerts. Only two suppliers are producing the critical component, and one of them has rolled faulty hardware off the assembly line.

Taptic engines from AAC Technologies Holdings, which operates in Shenzhen, China, have been found to "break down over time." According to the Journal, this led Apple to scrap some Apple Watches that had otherwise completed the production phase, a decision that has almost certainly affected the smartwatch's availability — but also prevented consumers from receiving malfunctioning devices.

Read next: Read our Apple Watch review.

Only two suppliers are producing the taptic engine, and one of them messed up

However, it's possible some faulty watches made it out into the world; in his review of the Apple Watch, Daring Fireball's John Gruber reported that he initially received a unit with a taptic engine that didn't function properly. At this time, Apple Watch shipping estimates are pushed back to June for all models and configurations.

Only yesterday, the company signaled that it plans to launch the smartwatch in other countries beginning in "late June." The Journal's report indicates that Apple has shifted most taptic engine manufacturing to its other supplier, Japan's Nidec Corp. Foxconn may also be tapped to help increase production of the Watch itself, though this wouldn't happen until later in 2015. The takeaway seems to be this: Apple Watch will remain hard to come by for the foreseeable future.