When performing a duplicate backup job of Sharepoint database resources from an incremental backup the job may hang indefinitely.
This issue is caused by the incremental backup job causing issues with the cataloging of the original backup if there is a mixture of recovery models of the Sharepoint SQL databases in that backup. When an incremental (log) backup is performed on SQL databases that are in a 'Simple' recovery model, no data is backed up because log backups are not possible. This creates a 'null' in the original backup so that when the duplicate job runs and this 'null' is encountered the duplicate job will hang attempting to retrieve a catalog entry that is not present.
The recommended solution is to set all Sharepoint SQL databases to 'Simple' recovery model within SQL Management Studio and perform only Full or Full/Differential backups and duplicates of Sharepoint resources.