A timeout (30000 milliseconds) was reached while waiting for a transaction response from the NetBackup Discovery Framework service.

Since a few weeks our eventlogs of several servers are polluted with error events as

A timeout (30000 milliseconds) was reached while waiting for a transaction response from the NetBackup Discovery Framework service. Restarting the Symantec private exchange service (which will cause a restart of all nbu services)  solves the issue temporarely but after a few days the events appearing again. Somebody who has any idea of the cause or who has a solution ?

Backups jobs are still running fine.