[Bug] Affix / In This Article menu does not expand in Modern template

[BradBearden]

Describe the bug
In the modern template, the affix side nav ("In this article" menu) does not expand to show Heading 3 or more. Also, as I scroll down the page it does not highlight the section in the right menu to show my current focus.

To Reproduce
Confirmed steps to reproduce the behavior:

1. Create a page with the following headings:
   • Heading 1 (H1)
   • Heading 2a (H2)
   • Heading 2b (H2)
   • Heading 3a (H3)
   • Heading 4 (H4)
2. Build your site using the Modern template
3. In the "In This Article" side menu, click on "Heading 2b"

Expected behavior
I would expect that clicking on Heading 2b in the "In This Article" section would cause "Heading 3a" and "Heading 4" to be displayed under it, slightly indented.

I would also expect "Heading 2b" to be highlighted. Likewise, if scrolling through the page, I would expect the sections in that menu to highlight and expand based on my current location in the page. (I believe this has been reported under #8539)

Screenshots

Context (please complete the following information):

• Browser: Chrome
• Form factor: Desktop
• Docfx version: 2.67.0.0 (upgraded from 2.56.2)
• Template: modern

Additional context
This may be related to #8539, or it may be a separate issue.

[lanthonyneville]

Any news about this?