iPad displays Apple logo with progress bar after updating or restoring from backup
If your iPad contains a large number of imported photos, it may display an Apple logo with a progress bar for a long time after updating or restoring from backup.
When this occurs, the progress bar may appear to be either frozen or moving very slowly.
The progress bar indicates that the iPad is migrating user files for use with the current version of iOS. While this process can take as little as a minute, when an iPad contains a large number of imported photos, the process can take several minutes to an hour to complete. The amount of time depends on the number of imported images and the format they are in (JPG, PNG, RAW, and so on).
If this occurs, verify that the update or restore from backup has completed in iTunes.
If your iPad appears in iTunes and allows you to configure sync options and sync content, the update/restore process is complete. Leave your iPad connected to iTunes and wait for the migration process to finish.