Please refer to the following technote. I suspect the issue that you are facing is as per the technote
http://www.symantec.com/docs/TECH191450 : Sharepoint Granular Recovery Technology backup to tape runs excessively long in 'updating catalogs' status.
Try to Test the Workaround from the technote
Run non-GRT backup to tape or run backup to Backup-to-Disk folder.
the backup job of sharepoint is a backup-to-disk and not to tape, it runs on deduplication disk storage and the following data meta index catalog job (due to GRT enable) runs very very slow (it takes more than 2 days)