Sections getting different ids from their headings

Description of problem

URL to affected spec or repo:

https://w3ctag.github.io/privacy-principles/#hl-sensitive-information

What happened (e.g., it crashed)?:

The source for this heading is

## Sensitive Information {#hl-sensitive-information}

This generates:

<section id="sensitive-information"><div class="header-wrapper">
<h3 id="hl-sensitive-information"><bdi class="secno">2.4 </bdi>Sensitive Information</h3>
<a class="self-link" href="#hl-sensitive-information" aria-label="Permalink for Section 2.4"></a> ...

This causes https://w3c.github.io/webref/ed/headings/privacy-principles.json to omit the id that the self-link refers to. (Filed as https://github.com/w3c/reffy/issues/1824)

Expected behavior (e.g., it shouldn't crash):

Only 1 id should be generated for this section/heading, and it should match the id assigned by the custom heading id.

Reproduce the heading case from the linked privacy-principles index.html source, including ## Sensitive Information {#hl-sensitive-information}. Trace ReSpec’s heading generation and custom heading ID handling, then verify the rendered section and heading produce one matching id and that the resulting headings JSON retains the self-link target.