NNMMedi: backups fail for some segments "Unable to verify caller privileges: Timed out"

NetWorker Module for Meditech Image Service Backups (ISB) started failing for some segments at random with the error:

YYYY-MM-DD HH:MM:SS PM  nsrmedisv NSR notice D:/views/nw/19.9/nsr/db_apps/NMMedi/nmmedispawn.cpp(584): Job 2159949: 204808:save: The backup has failed because saveset id ########## is marked as failed or suspect or is missing in the media database.
YYYY-MM-DD HH:MM:SS PM  nsrmedisv NSR notice D:/views/nw/19.9/nsr/db_apps/NMMedi/nmmedispawn.cpp(584): Job 2159949: 7167:save: save completion time: YYYY-MM-DD HH:MM:SS PM
YYYY-MM-DD HH:MM:SS PM  nsrmedisv NSR notice D:/views/nw/19.9/nsr/db_apps/NMMedi/nmmedispawn.cpp(658): Job 2159949: Exited with exit code 5
YYYY-MM-DD HH:MM:SS PM  nsrmedisv NSR notice nsrmedisv(396): Save job 2159949 status completed
YYYY-MM-DD HH:MM:SS PM  nsrmedisv NSR critical nsrmedisv(5046): Could not get save set id  for job 2159949. It failed with error: [Unable to query save set time ##########: Unable to verify caller privileges: Timed out]
YYYY-MM-DD HH:MM:SS PM  nsrmedisv NSR warning nsrmedisv(413): Backup failed for SRV_NAME E: Save job status error.
YYYY-MM-DD HH:MM:SS PM  nsrmedisv NSR critical nsrmedisv(976): Error performing backup for Meditech_ISB. nsrmedisv(2927): Some of the MEDITECH volumes failed to backup in Meditech_ISB.

Suggested actions:
 

• Ensure that the NetWorker server, storage nodes (if used), and client are using optimized OS settings: NetWorker: Best practices for networking configuration
• Delete/Remove retired clients from NMC:
  • Typically if there are many decommissioned clients, performance impacts are observed on the NetWorker Server Daemon (NSRD):
    • NetWorker: NSRD takes a long time to start "checking resource types in the RAP database"
    • NetWorker: The NetWorker server intermittently becomes unresponsive
• Reduce the size of the media database by deleting old save sets, if no longer required:
  • NetWorker: Change Browse time and Retention of Multiple Save sets
  • NetWorker: How to delete Multiple or Individual SSIDs
• Redirect the backups to a new/another NetWorker Server with a smaller media database (if possible).