TOC Navigation no longer works on Kobo Libra Colour 4.44.23552

[DanteDT]

Specs mention EPUB 3 TOC navigation

The example given is:

<nav epub:type="toc">
    <h2>Contents</h2>
    <ol>
        <li><a href="title-page.xhtml">Title Page</a></li>
		<li><a href="copyright.xhtml">Copyright</a></li>
		<li><a href="chapter-1.xhtml">Chapter 1</a></li>
		<li><a href="chapter-2.xhtml">Chapter 2</a></li>
		<li><a href="chapter-3.xhtml">Chapter 3</a></li>
    </ol>
</nav>

Kobo Libra Colour 4.44.23552 software ver fails to load or fall back to any navigation TOC for multiple epubs from a variety of sources.

Example nav.xhtml that Kobo fails to load as the single TOC in the epub.

<nav epub:type="toc" id="nav">
<h1>Table of Contents</h1>
<ol class="nav-toc">
<li><a href="title.xhtml">Title page</a></li>
<li><a href="ch001.xhtml">Chapter 1</a></li>
<li><a href="ch002.xhtml#sub001">Chapter 2</a><ol class="nav-toc">
    <li><a href="ch002.xhtml#sub002">Subtitle 1</a></li>
    <li><a href="ch002.xhtml#sub003">Subtitle 2</a></li>
</ol></li>
...
</nav>

This is consistent with the reference EPUB spec, like 7.3 The nav element: restrictions.

Yet this Kobo, this software version fails to load these TOCs or fall back to any TOC content, which remains empty.

Multiple other devices and apps load and display these TOCs without issue, and they are fully functional for navigation.