[KevinH]

The file names are ridiculous and something about them is making Sigil think they are not the same as listed in the opf manifest. I have not figured out why (yet). If you load the epub into Sigil, it will tell you that it is seeing these files as unmanifested. So the path in the opf manifest does not seem to match the path as created when extracting file from the zip archive.

If you unzip the epub, you can actually use AddExisting to import the entire set of files and save it as an epub, and then it will work.

So it may be an encoding issue in the content.opf itself as it appears it was edited by some tool that is insane enough to add a BOM (byte order mark) to a utf-8 file! There no big endian vs little endian when it is a stream of just bytes (ie. in a utf-8 file) and no ByteOrder mark is ever needed or ever used anymore.

I did notice the Sigil 1.7 metadata at some point in the content.opf so at some point this was edited with Sigil but Sigil will not write out BOM so something has edited it after that.