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taratears - that suggests something external to calibre is interfering, by restoring the library to a prior state
Which OS and are you using - Windows, OSX or Linux - and which version/flavour of
What version of calibre are you using - if Windows is it 32bit, 64 bit or Portable
Where is your library located - on a local drive, and/or a network device (server, NAS etc), and/or cloud storage (Dropbox, OneDrive, Google Drive etc). If it's anything other than local then that could be the cause, see ==>>
Do not put your calibre library on a networked drive.
Do you run any always on file synchronisation services - Time Machine, Resilio, Free File Synch's RealTime Synch etc.
BR