JupyterLab error "nbconvert failed: Pandoc wasn't found."

[adamcc]

I searched here and on https://discourse.jupyter.org/ and could not find an answer to solve this error.

When using the JupyterLab menu File > Save and Export Notebook as > PDF I get an empty webpage saying:

500 : Internal Server Error
The error was:
nbconvert failed: Pandoc wasn't found.
Please check that pandoc is installed:
https://pandoc.org/installing.html

However:

% which pandoc
/usr/local/bin/pandoc

and

which xelatex
/Library/TeX/texbin/xelatex

and even the command-line version works fine:

% jupyter nbconvert --to pdf 20221003_stringDB-more.ipynb
[NbConvertApp] Converting notebook 20221003_stringDB-more.ipynb to pdf
[NbConvertApp] Support files will be in 20221003_stringDB-more_files/
[NbConvertApp] Making directory ./20221003_stringDB-more_files
[NbConvertApp] Making directory ./20221003_stringDB-more_files
[NbConvertApp] Writing 22253 bytes to notebook.tex
[NbConvertApp] Building PDF
[NbConvertApp] Running xelatex 3 times: ['xelatex', 'notebook.tex', '-quiet']
[NbConvertApp] Running bibtex 1 time: ['bibtex', 'notebook']
[NbConvertApp] WARNING | bibtex had problems, most likely because there were no citations
[NbConvertApp] PDF successfully created
[NbConvertApp] Writing 4885238 bytes to 20221003_stringDB-more.pdf

So the error message appears to be misleading, at least with regard to the specific claims that pandoc isn't installed and that nbconvert isn't working.

Is this a bug or some specific issue with my setup?

[adamcc]

After some time and restarting Jupyter, it started working. No clear reason why.