
In the context of the photo deletion problem mentioned in the updates, Apple refers to the issue as a "rare issue" to indicate that it affected only a small number of users and a small number of photos. The problem, caused by database corruption, resulted in some photos not being fully deleted as expected, and reappearing in the Photos library even after being deleted. By calling it a "rare issue", Apple emphasizes that the bug was not widespread and has been addressed in the iOS 17.5.1 update.

Apple released a revised build of iPadOS 17.5.1 specifically for the 10th generation iPad because they likely found a bug affecting only this model. The new build number is 21F91, compared to the original build number 21F90. The revised build is only available for the latest entry-level iPad and hasn't been released for any other iPhone or iPad models.

The revised build of iPadOS 17.5.1 with the build number 21F91 is specifically for the 10th generation iPad and is not available for any other Apple devices, including other iPad or iPhone models3. It appears that this updated build was released to address a bug that might have been affecting only the 10th generation iPad.