Calibre reset metadata.calibre when device is plugged

Good morning everyone,
Whenever I connect my Kobo Aura One to Calibre, Calibre resets the metadata.calibre file by modifying it so that it always contains only 3 "books" (Plato, kfmon, koreader, that are JPG/PNG in truth), even after I have just loaded my books from the PC and have updated the metadata; I just need to eject and reconnect the device for metadata.calibre to be reset. The actual physical library is not touched, the book files remain where they are in perfect condition: only metadata.calibre is affected by this strangeness. I use KOReader as a reader, but the latter does not seem to cause problems: this strange phenomenon happens only to the plugin with the caliber running (tested various times). Certainly I am doing something wrong, but I could not find a solution by searching the net or working on the Caliber configuration menus.

Thanks to anyone who can give me some tips to fix it.
I use Calibre 6.4.0