Run Library Maintanence:
If it reports Missing
FORMATS (calibre believes those should be there), Something OUTSIDE Calibre is removing files, because the DB still shows the Formats that you had for the book.
If Calibre was used, those books would have been in step with the DB and no error.
If the entire book record (and book formats), there would be no error AND Someone did tell Calibre to 'delete' that title
The tag
News can have an auto cleanup if enabled.
Normal books should not have that tag used
