This issue never has a resolution posted here, unfortunately, but in seeing something similar again, we have resolved what was probably happening. A post about it actually exists here.
What seems to be happening is that a particular version of Matplotlib (3.1.2) has a known error about producing JPGs. Unfortunately, the Aptitude package manager in Ubuntu 20.04 by default installs exactly this version by default, so users who have used something like sudo apt-get install python3-matplotlib to install Python in Ubuntu 20.04 will likely have this issue. To check your Python's Matplotlib version number, you can run:
python -c "import matplotlib as mmm; print(mmm.__version__)"
If it comes out as "3.1.2", you will likely not be able to make JPG images successfully from Matplotlib, causing a few parts of the APQC HTML to be missing (those that use 1dplot.py, specifically).
To resolve this issue, you can install a different version of Matplotlib as follows:
sudo apt-get install pip
sudo apt-get remove python3-matplotlib
pip install matplotlib
--pt