Issue with Cover.XHTML in apple books

[Volcanic08*]

Hey, I have some custom ebooks I set up with covers. I added a cover.xhtml file so the cover loads first before any text in the book. This works fine in Calibre for all my books, but I use Apple Books to read on my iPhone, so no matter what storage service I use—Google Drive, Dropbox, etc.—sometimes the cover.xhtml file doesn't load, and it instead skips to the text. It's not all of my books, so I don't know what's going on. Anyone know how I can fix this?

I've attached, for example, 2 ePubs; Blood Oaths works just fine, whereas Nomad does not.

[Jaws]

There are two things "wrong" with the Nomad epub, both fixable (one annoying to do). I can't test it against the Apple system, but either or both of these might be causing the problem.

First, the easy one: When opening the Nomad epub in the Calibre editor, the cover.xhtml file is not marked as the cover. Right-click on the filename (cover.xhtml) and select the option "Mark cover.xhtml as cover page." Save the ebook in the editor, close the editor, and reopen the ebook in the editor.

Now, the annoying one: Sometimes the read-order settings don't get automatically updated, even after marking cover.xhtml as the cover. In the Nomad epub, these are in the file (in the bottom group) toc.ncx. You may need to manually edit this to add the cover.xhtml file as playOrder 1, and then manually iterate all of the other playOrders and navPoint ids. Insert the following at line 14 in toc.ncx:

    <navPoint id="num_1" playOrder="1">
      <navLabel>
        <text>Cover</text>
      </navLabel>
      <content src="cover.xhtml"/>
    </navPoint>

Then manually go down the rest of the toc.ncx file and, on the line for navPoint id, iterate both (so Chapter 1 has

<navPoint id="num_2" playOrder="2">

Changing out the id name may not be necessary, but as long as you're having to manually edit anyway...

[theducks]

I think Calibre fixes the number upon save.
I just remove the section and it seems to be fine.

[DNSB]

I'm just going to say that Nomad is an unadulterated mess. Look at line 164 in the Nomad_split_006.xhtml file. Paragraphs filled with RLM characters (why are they adding strong R to L on what is basically English text? Zero width joiners everywhere, paragraphs ended by pair of <br class="whatever">, use of strike which has been deprecated for ePub though the calibre class using line-through is correct. Not to mention in the stylesheet, calibre9 uses text-align: LEFT; which is incorrect since that should be text-align: left; (case sensitivity, you know).

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As for Blood Oaths? It has more than enough errors in the .opf file that I didn't bother doing more than a cursory glance at the rest of the file.