iMore reports that Apple has just released a new build of its iOS 9.3 update after the original version was found to have been causing activation problems on older devices. The new build is 13E236, and is only for older devices, so if you managed to install the initial update on your newer device without any problems, then there’s no need for you to download this update.
Yesterday Apple moved to pause the initial update after some owners of older devices such as the iPhone 5s and earlier and iPad Air and earlier reported that they were having problems activating their phones after they had installed iOS 9.3. The issues emerged when users were required to enter their Apple ID and password that they had initially used to set up their device during the update process. Some users who were unable to remember that original password found that the iPhone or iPad would be inactive unless they could recover or reset their password. The newly released updated version of iOS 9.3 ensures that this process is no longer necessary.
Sources: Apple issues new build of iOS 9.3 for older devices that fixes activation issues
Apple pausing iOS 9.3 updates for older devices, working on activation fix