I looked at the hrefs in the book file via strings and found this is the path that they are looking for:
So of did links (symbolic) to Text -> text and also Images -> images and it still does not work. I think you might have other code looking or pointing elsewhere. If you are going to support cross platform, Linux and MacOS are case sensitive, I don't think windows is when it comes to path decelerations. You might want to check all your source code and do a bulk case change lower or upper, and see if that does not solve some of the issues you have been having.
This might not be because of you, it would be wxpython or some library that is causing the issue. I have run into this before using 3rd party libs. It's a pane if it is someone else’s code, then you have to check it every rev unless you can get them to fix the issue.
Oh the joys of code.
.\\itch - I am just an old guy who knows some stuff.