Comment 6 for bug 1898394

Sorry to reopen this old one... I am seeing this behavior consistently with all books, from all sources, when working with AZW3 file formats.

Calibre version: 5.7.2
OS: Windows 10 x64 (build 19042)

This includes original content as well as content in MOBI and EPUB from other sources. I have completely removed all plugins.

For the current example, I am using an EPUB file from TOR (their monthly free download of Seanan McGuire's "Come Tumbling Down"). I haven't modified this EPUB in any way, and it works great, no problems. The ToC is fine. When I convert to AZW3, all ToC entries that had been pointing to "top of page" now point to an invalid id that is a GUID autogenerated by Calibre. This id does not exist anywhere in the files. If I manually edit the ToC to return it to top of file, the ToC looks good again, but after saving, closing, and re-opening, there is a new invalid autogenerated GUID id and the ToC entry shows the error.

It's not just this book; it's ALL books since the release of 5.x, including books from MOBI sources and self-created books.

I will also upload images.

Thank you for all your help, and let me know if there are any diagnostics I can help provide.