I have an iPhone 6 currently running iOS 8.4.1. I have attempted to upgrade to iOS 9 both on the phone (through the Settings app) and also via iTunes. I have also tried wiping the phone and restoring using the iOS 9 .ipsw. Every single time the exact same thing happens:
- The initial part of the install appears to happen normally, without a problem. When I am doing it through iTunes, the progress bar in iTunes completes and disappears as iTunes waits for the phone to reboot.
- The phone reboots. The apple logo appears on the black background, but nothing happens. There is no progress bar below the logo. (On older iOS versions like 8.4.1, a progress bar appears to complete the installation after the first reboot.)
- I have let the phone sit in this state for over 5 hours and nothing ever changes.
- The phone does not respond to the power button. I have to hard-reset it by holding the power and home buttons.
- Once the phone resets, it immediately goes to the screen that requests it be plugged into iTunes.
- When plugged into iTunes, I get a generic message saying that there is a problem with my iPhone and that I either need to update or restore & update.
- The only way to get the phone to a functional state is to manually restore to the old 8.4.1 .ipsw file.
These symptoms appear to be distinct from both the well known "Slide to Upgrade" issue. It may be related to the infinite reboot loop issue, but it seems distinct because iOS never actually finishes the installation and no progress bar ever appears upon reboot.
