Do a search for the multiple warnings about not putting your library on a cloud drive. Sooner or later you will have issues. With Google Drive, the errors will be immediate since Google Drive uses (numbers) at the end of names for revisions while calibre uses that for the book's internal ID.
See
I am getting errors with my calibre library on a networked drive/NAS? in the calibre FAQs and
SQLite Over a Network, Caveats and Considerations on the SQLite website for more information.