[Sabardeyn]

Since you asked, this is a completely wild guess...

You said the Library was stored on an SSD. I know that some of the early SSDs had an issue with file read/writes/deletes because of the way an SSD handles things. For instance, it would mark a file deleted and then wait a variable amount of time before actually removing the file. This timing delay was causing issues for lots of SSD owners and the system was improved in the next generation of SSD products; it's something built into the hardware (BIOS equivalent), I believe.

So perhaps there is some kind of issue here between either the Mac OS/SSD/Calibre? Or you've got an older SSD with the timing issue?

I would suggest starting by finding out the make & model of your SSD and checking online if there are any known issues with it specifically. As well as checking for your version of the Mac OS having SSD errors (in general). If that doesn't result in any viable avenues for further research, continue reading.


To verify it's an SSD related issue, test whether this error continues to occur on a 2nd Library on another drive (different make & model SSD, HDD, USB Flashdrive, internal/external, etc).

I don't recall you mentioning how quickly you saw errors, or a possible trigger for the problem. So the testing time might be substantial (months), as you use this 2nd Library normally. The more/longer you test things, the greater the chance you'll encounter the trigger and track the problem down.

Use the 2nd Library as normal, ignoring the 1st Library completely. Do all your normal work in the 2nd Library. Back up the 2nd Library daily so you don't lose any work (2-3 copies of backups in case errors don't appear for a day or so). Check daily (before and after doing any edits?) to see if the errors you saw with your 1st Library are occurring with your 2nd Library. If you do see errors, try to think what you did to the ebook that has the error. By checking daily you can spot the error quickly and stand a better chance at remembering what you did that might have triggered things.

I realize I'm suggesting a long and complicated process, but as I said, it is the only thing I can think of. Perhaps someone else has a better way to handle this testing?