Table of contents doesn't show up in Kindle Previewer

I'm creating an ebook in Sigil, and then converting it to Kindle format using the Kindle previewer.

When I view the book in the Kindle Previewer, I cannot access the table of contents from the "view all" menu. Earlier versions of this book, I was able to do that. I think the problem started when I added pages in Sigil.

I've had a look at content.opf and I can't see anything wrong. The TOC is listed in the guide section: <reference type="toc" title="contents" href="Text/contents.xhtml"/>

When I test this book on a Kindle device, I can go to the table of contents using the "go to" menu, and I can jump from chapter to chapter using the next chapter buttons. So the logical toc seems to be working.

It just makes me nervous that this book is displaying differently in the Kindle Viewer, as if there's something wrong with it. Am I being paranoid?

I've attached screenshots of what the book looks like in the Kindle Previewer, the first screenshot shows the book as it is now, where I cannot access the TOC and only one page is shown. The other screenshot shows the book as it used to be, where I can access the TOC from that drop down menu, and the other pages are displayed as well.

Any advice much appreciated.

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