This error is caused by the VM’s unique inventory reference identification number (MOREF, or Managed Object Reference) changing within the virtual infrastructure, or the VM having been deleted. Veeam is still attempting to find the VM by its old reference ID number based on a “find vm by NAME where REFID = X” query.
Note: The most common events that cause a VM MOREF ID to change are:
*Veeam Backup & Replication caches infrastructure information to improve performance, the refresh function purges the cached data. The refresh function must be used when resolving this issue.
Resolution can be confirmed without running the job. Edit the job, navigating to "Virtual Machines" and click the [Recalculate] button. Note that the VM's whose MoRefs changed now report as having the correct size.
Please be aware that VM's are tracked by their unique MoRef ID. When the MoRef changes the VM is considered an entirely different VM. As such Veeam Backup & Replication will treat them accordingly and create a Full restore point for the "new" VM.