Apple has just released iOS 8.0.1, a bug fix update for iOS 8. Unfortunately, while the full binary installed from iTunes worked fine, the bit-differential file installed over-the-air via Software Update has left some iPhone 6 and iPhone 6 Plus with Touch ID and cellular connection issues. Apple has since pulled the update, but that doesn't help affected iPhones. It's possible Apple can fix and re-issue the update quickly, or a workaround will be found shortly, but if you've already updated, and you're affected, here's what you need to do:
Update: Apple has released iOS 8.0.2 to address the errors. No need to downgrade any more.
- Turn off Find my iPhone via Settings > iCloud
- Download iOS 8 for iPhone 6 or iPhone 6 Plus
- Make sure you're on the latest version of iTunes. Go to About and then Check for Updates or visit iTunes.com.
- Launch iTunes on your Mac or PC.
- Connect your iPhone 6 or iPhone 6 Plus to iTunes via Lightning to USB cable.
- Hold down Option (Mac) or Shift (Windows) click on "Check for Update".
- Choose the iOS 8 firmware file (.ispw) you downloaded in step 2.
- Let iTunes do its thing
- Once you're back up and running Turn Find my iPhone back on.
If you can't turn off Find my iPhone or are otherwise having trouble, put your iPhone 6 or iPhone 6 Plus into DFU mode first and then Restore with iTunes. (You can restore again from your last iCloud backup later to get your stuff back.)
If you still have 8.0.1 waiting to install and you want to get rid of it, go to Settings > General > Usage > Manage Storage and delete it.
At this point you should be back up and running again with full Touch ID and cellular service. Yes, this is frustrating and annoying but it's also the fastest way we've found to get back up and running if you've already updated to iOS 8.0.1 and are experiencing issues.
Give it a try and let me know if it works for you!