I have the problem with Jupyter notebook version 6.1.4. After installing nbextensions
and enabling extension "Table of Contents (2)" (as "toc" and "toc2" don't work), I cannot obtain the TOC of an a notebook (2.8 MB), while new notebooks have a table of contents.
Reloading, reopening, restarting jupyter does not help, even after a long wait (> 15 min).
I have tried with browsers Mozilla Firefox version 83 and Chromium version 87.
However, a workaround is to create a new notebook (with TOC), then copy all cells from old notebook to new notebook. In order to do this, this might be useful:
Actually I could not copy all cells at once, I had to do three partial copies.
Alas, my method is not only painful but also ineffective in the long term, as the TOC disappeared again.
Restarting the computer worked or did not work.
Opening a small notebook with a table of content and reloading the big notebook worked or did not work.
The problem concerns all Nbextensions, they are just not active for the big notebook. A Javascript console is shown in Google Chrome with Control Shift J.
Error: Load timeout for modules:
nbextensions/nbextensions_configurator/config_menu/main,nbextensions/init_cell/main,nbextensions/spellchecker/main,nbextensions/toc2/main,nbextensions/jupyter-js-widgets/extension