In rare cases, when a media file has been offloaded and you try to open it by clicking directly on the file in SharePoint (one-click restore), SharePoint may display a message indicating that the file preview is not available.
In this situation, the file is still archived correctly, but the automatic restore via preview does not complete successfully.
You can restore the file using an alternative ShArc restore option.
Go to the document library that contains the offloaded media file.
Click the three dots (⋯) next to the file to open the file menu.
In the file menu, select:
Open → Restore with ShArc
This starts the restore process using ShArc directly, instead of relying on the file preview.