A backup job pointed at ReFS 3.0 based repository fails with “The request is not supported. Failed to duplicate extent"
The error is generated if the cluster size for the ReFS volume was changed recently. The job may be successful on incremental/active full runs, but fails on synthetic operations (this includes an incremental run of a Reverse job)
Simply opening the affected repository’s settings in the Veeam console and pressing Finish will force the new volume parameters to be re-synchronized with Veeam database and allow the backups to run normally again.