odd header in the html output. misconfiguration ?

[parmentelat]

Bug Report

Describe the bug

all my html output pages have a weird-looking header

all my pages have this, see a live example here
https://ue12-python-numerique.readthedocs.io/fr/latest/0-01-intro.html

Minimal Notebook Example

it doesn't seem to belong in a specific notebook
more helpful maybe, my sphinx config is here
https://github.com/ue12/python-numerique/blob/master/notebooks/conf.py

Expected Behaviour

this fragment probably should go through processing and display a standard header;
maybe something like this (captured on a similar document from last year)

Runtime Information

this is on the standard readthedocs python-3.x build image

• Versions of any other relevant python packages

Additional context

Here again i am a little confused as to any potential tweak that I might have made in the overall config (conf.py, json for the extension, my own extensions...);

I digged in my history, it seems like this has always been the case with that particular project, so I take it it's a misconfiguration that I created when I cloned my course from last year (the one I showed in the expected behaviour section)

Logging

n/a

sorry for the hassle :)
nothing crucial here, I can live with that
Thanks !

[parmentelat]

for the record, it's odd that I get this undesired addition on readthedocs and not when I run sphinx locally on my mac