While using Quality Check to find invalid title_sorts, I noticed that fanfics that have their titles "surrounded in quotes" show up as a failed sort, only the closing quotation mark appears in the title_sort. Is this a FFF issue or a Calibre one?
Here's one of the stories it happened on, with the first part replace_metadata'd out:
https://archiveofourown.org/works/34520701
I'll PM you another example that doesn't require a replace_metadata (but is also not family-friendly).