Ah, this only happens in one instance. When 'XX' is displayed in the ToC, it only happens where there is link directly above the heading:

.. _Prepare:

:index:`Preparing` the |prodname| for use
#########################################

Actually, it seems any directive before the heading causes this issue, for example:

.. raw:: html
...

@brechtm is this a rinoh issue or something particular to my install?

The XX basically means that rinohtype can't resolve the reference or page number. I'll need to investigate to see what's happening exactly. Thanks for the extra info!

I can't reproduce this (tests-regression/sphinx/test-ref/chapter1.rst - project zip). It could also be a Sphinx bug that's already fixed (I tried with 5.3.0). If you still see this with Sphinx 5.3.0, please provide a minimal Sphinx project triggering the bug.

This occurs with Sphinx version 6.0.0b3 - I will retest with 5.3 and let you know the results

Same thing happens with Sphinx 5.3:

Do you want me to send my demo instance?

Do you want me to send my demo instance?

Yes, please.

OK...here it is. Bear in mind this is the content I was using for the pdf rear page development, so its a bit all over the place. However, I have edited the hands.rst file to add an index entry:

.. _Prepare:

:index:`Preparing` the |prodname| for use
#########################################

test text

General health and safety
#########################

Hope this helps!

pdf-dev.zip

Thanks, that helped! Turns out this only happens with index terms in section titles that are rendered out of line (BodyPageTemplate.chapter_title_flowables). For the book template (and your derivative), that means chapter titles. In some cases, it does output a page number, possibly a wrong one, and the hyperlink is broken. Not yet sure how to fix this...

Now I'm aware of the issue, it isn't a problem (I will not add an index entry to a heading where there is a directive preceding it), but if you can find a fix, that would be great (as I am bound to forget about this!)

I will not add an index entry to a heading where there is a directive preceding it

To be clear: the issue isn't caused by the directive preceding it. It happens when the index role is used in a chapter title. This is because chapter titles are rendered in a different way (in the Book template, at least).