Apple today has stopped signing iOS 12.1.3, which means it is no longer possible to downgrade from iOS 12.1.4. iOS 12.1.4 was released last month to resolve the FaceTime eavesdropping bug.
Apple generally stops signing older releases of iOS within a few weeks of an update being made available. Most recently, Apple stopped signing iOS 12.1.1 and iOS 12.1.2 last month.
iOS 12.1.4 was released just over a month ago following the discovery of a huge Group FaceTime bug that would allow someone to eavesdrop on another user. Apple also disabled Group FaceTime on older versions of iOS, such as iOS 12.1.3, to prevent the bug from affecting users.
Apple is currently beta testing iOS 12.2 with new Animoji characters, enhanced TV functionality in HomeKit, Apple News support in Canada, and more. iOS 12.2 is likely to be released later this month, likely in conjunction with Apple’s March 25th event.
At the March 25th event, Apple is expected to introduce its new Apple News magazine subscription service, as well as enhancements to its TV app. Both of these are software-based changes that would likely be included in iOS 12.2.