Unfortunately, the changelog did not reveal exactly what kind of changes or fixes Apple has made, but either way, hopefully, this update will address whatever problem you are having with your iOS device now. The update should be available for download, so head on over to your Settings in your iOS device to get your hands on it.
That being said, the folks at ArsTechnica have confirmed that while this is an update with bug fixes, Apple has yet to address the battery percentage bug that was reported on recently. For those learning about this for the first time, there is a bug affecting the iPhone 6s/6s Plus in which the battery percentage disappears when you change time zones and adjust the time manually.
Apple has offered up some workarounds but obviously, this isn’t a permanent solution to the problem, but, either way, the fix is not in iOS 9.2.1 so we guess iPhone 6s/6s Plus owners will have to wait for it in a later release, hopefully, iOS 9.3.