As is customary following an iOS software update, Apple has made steps to ensure folks can’t go back to version 9.2.1. With iOS 9.3 and 9.3.1 released, Cupertino has stopped digitally signing the older version of the operating system, 9.2.1.
The release of iOS 9.3 was marred with early problems for some
In spite of how smooth the upgrade was for owners of newer devices, the upgrade path was quite rocky for owners of iPad 2 devices. After upgrading their tablets to iOS 9.3, many owners of the iPad 2 found themselves unable to activate their devices. This effectively bricked the devices. Apple responded quickly, pulling the iOS 9.3 package for those devices and replacing it with a new one that worked fine.
But wait, there's more
As if that weren’t enough, some Sprint users experienced problems connecting to LTE data services after updating to iOS 9.3. Fortunately, that issue was quickly resolved with a carrier settings update, but users who never or rarely plugged their iPhone devices into their computer might not have been aware of the available patch.
That wasn't the end of the problems
Unfortunately, that wasn’t the end of the problems, or even the least of them, for iOS 9.3. Next came the dreaded Safari link bug, which caused apps to crash or hang when users tapped on Web page addresses. Many users experienced the problem, and were unable to open links inside of apps including Safari, Messages, and Mail without those apps crashing. Third-party apps, such as Booking, were also culprits in the débâcle. The update to 9.3.1 seems to have resolved all of these issues.
Since those issues have been resolved, it seems that iOS 9.3.1 is quite stable. I think Apple is acting a bit quickly in removing the downgrade path, but I understand why Cupertino wants to prevent device owners from going back to the security vulnerabilities of iOS 9.2.1. Let’s just hope no new problems surface with the latest and greatest version of iOS.