If it has never worked, I would sit with the Domain Admin and go through each step in the manual to check and validate all requirements.
Most of the time we find that a single step has been missed in the process.
The manual starts off with high-level steps, with reference to another section of the manual that contains the details:
■ The Network File System (NFS) must be installed on the media server and all
Active Directory domain controllers or ADAM/LDS hosts.
See “About installing and configuring Network File System (NFS) for Active
Directory Granular Recovery” on page 1214.
See “About configuring Services for Network File System (NFS) on Windows
2012, 2012 R2, or 2016” on page 1215.
See “About configuring Services for Network File System (NFS) on Windows
2008 and 2008 R2” on page 1223.
■ The NetBackup Client Service must be configured to log on as an account with
domain privileges.
To perform granular backups and restores of the Active Directory, the NetBackup
Legacy Client Service (bpinetd) must run under the domain administrator
account on the Active Directory domain controller or ADAM server. By default,
bpinetd runs under the Local System account.
See “Configuring the NetBackup Client Service” on page 1148.
For information on the media server platforms that support Granular Recovery
Technology see the NetBackup compatibility lists on the Veritas NetBackup
Hardware Compatibility List (HCL).
If all config items have been checked and verified, you will need to dig into the logs to see where the process failed.