Sorry, I don't recognize any such recommendation to 'mirror' or any suggestion that mirroring (deleting 'orphan files') will improve a situation where it is trying to copy a file from Source to Destination (thus, not trying to delete an orphan file). You may need to provide the exact wording (even better, a screenshot)
If you prefer, you can raise a support ticket via the Contact Supports links here. You may find it easier to attach files, etc., via that means
If you prefer, you can raise a support ticket via the Contact Supports links here. You may find it easier to attach files, etc., via that means