Bug: TOC heading is wrongly numbered as sub-section

Here is the TOC.

The last h1 should be a new section, but is being detected as a sub-section.

Here is the code generated in the gutenberg editor:

<!-- wp:heading {"level":1} -->
<h1>h1</h1>
<!-- /wp:heading -->

<!-- wp:heading -->
<h2>h2</h2>
<!-- /wp:heading -->

<!-- wp:heading {"level":3} -->
<h3>h3</h3>
<!-- /wp:heading -->

<!-- wp:heading {"level":1} -->
<h1>h1</h1>
<!-- /wp:heading -->