Header on the sidebar will disappear if followed by ipynb in the _toc.yml

Describe the bug Header will disappear after clicking on the first file whose type is ipynb. For example, the _toc.yml is as the following, notice that “1_1.ipynb” is an “ipynb” file not “md”.

- file: intro.md

- header: Chapter1
- file: 1_1.ipynb
- file: 1_2.ipynb(md)

After compiling to html, everything is OK. If click on the 1_1 in the sidebar, after page refreshed, the header “Chapter1” will disappear, only shows "1_1, 1_2, ". But no problem if click on the 1_2 in the sidebar.

You can see from the screen shot before and after clicking on “Matplotlib” on the sidebar.

The header “Packages” dissappears.

If click on python (also an ipynb), the head “Packages” will come back.

To Reproduce Steps to reproduce the behavior:

1. Add an ‘ipynb’ file right after and header in “_toc.yml”.
2. Build
3. Open the html and click on the “ipynb” file on the sidebar
4. See “header” disappear.

Environment (please complete the following information):

• Python Version 3.7
• Output of jupyter-book --version

Jupyter Book: 0.7.0 MyST-NB: 0.8.3 Sphinx Book Theme: 0.0.23 MyST-Parser: 0.8.2 Jupyter-Cache: 0.2.2

[LinkHS]

so, just to be clear then, deleting _build doesn’t fix the problem?

No, it doesn’t work.

[choldgraf]

so, just to be clear then, deleting _build doesn’t fix the problem?