the scan time hints that the metadata.calibre file is missing.
Calibre write 2 files in the root of the drive (as appears to the PC) at the completion of the scan. These identify both the Calibre (Library) that did the scan and where things were found. LEAVE THEM ALONE (unless you want to do a full scan again

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Can you see the Books (or whatever it is called ) from the PC?
(Direct to device downloads may not be accessible to the PC)