When a virtual machine is restored by an instant restore operation, a snapshot is created to store all data that were written to the virtual machine disks. When the restore is completed, the ESXi host deletes the snapshot. The snapshot for the specified virtual machine could not be deleted.
Operation continues.
Examine the vSphere log to determine why is it not possible to delete the snapshot and resolve the problems that prevent the deletion. Then, delete the snapshot by using the snapshot manager.