Here's another data point regarding A03's 525 error. Trying to update this fic:
https://archiveofourown.org/works/61...ters/157176058
Calibre has 27 chapters and the index and chapters show chapter numbers. If I adjust the page on A03 to show Entire Work, I can download an epub with 28 chapters. However, chapter numbers are missing from the TOC and the file. Not sure if this is relevant but it's something ...
What a pain right now.
Stephen