From an R notebook, this is what I see when I try to export the Notebooks to PDF: nbconvert failed: xelatex not found on PATH, if you have not installed xelatex you may need to do so. Find further instructions at https://nbconvert.readthedocs.io/en/latest/install.html#installing-tex.
You might want to add latex to the docker image.
I also see an error page after downloading the notebook -> 500 : Internal Server Error. The notebook seems to download, though.
The export to HTML to my local computer seems to work fine.