I had a different error but my Calibre died after updating to 3.19 also? I could still find the library but I think it said it was very corrupted. I had a full-on crash and really couldn't recover, so I installed 3.17, added all my books back in, and then fixed all the missing info like custom columns.
I had an issue with an update a while ago too, maybe 3.07 or something around there.
Edit: the timing may have been a coincidence, idk.
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