Backup files moved between extents of a SOBR must always be placed in the same relative folder structure to the path of the extent.
The Scale-Out Backup Repository below is named "SOBR," there are 2 extents, “SOBR Extent 1” and “SOBR Extent 2”. Their "repository paths" are different, but if files are to be moved between them, the subfolders in those paths must remain the same.
In this example, "SOBR Extent 1" has a path of E:\VeeamBackup\, and "SOBR Extent 2" has a path of C:\Backups\. If the backup files are initially in E:\VeeamBackup\DailyBackup when they are moved to SOBR Extent 2, they must be placed in a folder named "DailyBackup" (C:\Backups\DailyBackup).
If a new extent is added to the Scale-Out Backup Repository, and you want to move some/all of the files from the existing extents, you would have to create the same folder structure. Then place a copy of the vbm from any other extent, and proceed with moving the files you intend to move to this extent.
For example, if an NFS share were added as the third extent of the SOBR example above with a path of backupnas:/backups/, then the full path to the manually moved backup files would have to be backupnas:/backups/DailyBackup/ for the files to be recognized correctly.