Backup DAG Failure

Goodmorning everyone,

We have an error in our automated backup of our DAG.
Sometimes it fails totally, sometimes like this example below, it works with warning and errors.

Avamar version : 19.7
Exchange version : 15.1

Here are my errors :

avtar Warning <16147>: AuthzInitializeContextFromSid failed: 2
avtar Warning <18051>: Could not determine privileges for user ********
avexvss Warning <42409>: Unable to retrieve backup history for this client.
avexvss Warning <13081>: No preferred DAG servers specified -- using default server list.
avexvss Error <0000>: Unable to connect to the remote client '##.##.##.##', error code: 2. Please ensure that the remote backup agent is running.
avexvss Error <12758>: [DAG] is unable to forward CTL sub-workorder to [Exchange].
avexvss Error <12967>: Remote client Exchange failed to start its subworkorder.
avexvss Error <41449>: Remote client Exchange is unable to proceed with backup because another backup is already in progress.
avexvss Error <0000>: The remote client Exchange failed to create VSS snapshot in predefined time.
avexvss Error <12977>: The remote client [Exchange] has failed to backup, so its components will not be displayed for restore.
avexvss Warning <18193>: Federated backup had exceptions, check log file(s) for details.

Thank you in advance for any assistance.

Have a great day

Bo0x