Hi everyone:
have the same issue on one of our iPhones. Mac Air 11" on OS X 10.11.4 iTunes 12.3.3 and an iPhone 5
The 9.3 update did not work. The device freezes ! I did not even get to an put screen.
Had to restore the iPhone and did it via Itunes with regular restore procedure Hold on/off and Home until iTunes sign showed up etc.
the I restored to 9.2.1. got my backup, I made just before update attempt.
Everything is fine unless, system has a update Info on General info but tells me that the current version is the lastest when trying to update.
Restartet all systems, changed USB port and did the again. No success. even deactivated reactivated system in Itunes store and iCloud.
After that new attempt, same result.
No Idea no error code . At least the iphone does well on 9.2.1. However it all started with a messed up upgrade attempt.
Apple used to have better quality !
Will let you know if I find any help in easter eggs or elsewhere, support while searching is welcome though.
Ralf