Unrestored attachments after "Restore Shortcut" job

Hello,

We did job "Restore shortcut" to restore attachments back to user mailboxes, so they can be exported into pst. However, some attachments (most old) remain unarhived in format attachment.pdf.html. The job was completed successfully. What caused this? User's mailboxes might was reconnected to different ad account (but that is just my guess). Attachments are not accessible also via EMC service account, that have full access for every mailbox. How can we proceeed? What else can cause this?

BR,

Jan