Possible Causes:

1. Hardware failure in the hard drive or storage drive

2. Antivirus scanning the drive which is B2D location or Recovery location or both.

3. VSS Snapshot failure

4. Slow network performance

5. Database corruption

• Check the compatibility by running B2D test.
  Please refer Backup-to-Disk Best Practices and how to perform B2D test https://www.veritas.com/support/en_US/article.100025225
  https://www.veritas.com/support/en_US/article.100020569

• Target the backup job to different disk storage

• Evaluate whether the problem can be resolved by the latest firmware updates or was triggered by a recent firmware update.

• Offline defrags may fix the problem in the unlikely case that the problem is due to an index consistency problem.

• Make sure the recovery location is un-compressed drive on the backup server (If the backup is tape, need to check in Exchange server)
  General tab on the Properties menu and un-check the box "Compress this drive to save disk space." Then click "Apply" and "OK." Your computer will now decompress the C drive. Always take backup of important files and folders in the drive before decompress the drive

• Clear the snapshots and reclaim the free space.
  Open a command prompt as administrator and run the command
  "vssadmin delete shadows /for=c: /all"
  Please refer https://www.veritas.com/support/en_US/article.100022885

• Need to run network test to make sure the network speed is good.

• Check the event viewer for the database related issues.

• Check the health of the databases ( repair as needed with the assistance of Microsoft)

• Run Non-GRT backup.
  
  Note: Any changes with the environment may require contact of of Microsoft or the respective hardware vendor.