Do not rely solely on the user interface error string. Navigate to the Veeam log directory to find the specific stack trace. Open C:\ProgramData\Veeam\Backup\ . Locate the folder named after your failing backup job. Open the Job.Backup.log file using a text editor.
In some instances, the overflow error is purely cosmetic or related to how the Veeam console processes data visualization. veeam backup and replication overflow error
If you manage thousands of workloads, deploy Veeam v12+ using PostgreSQL, which handles massive configuration data scales better than SQL Server Express. Do not rely solely on the user interface error string