MathJax alternate renderer issues in notebook rendering

In a fresh install from conda-forge (jupyterlab 3.1.14 and its deps, in an isolated conda environment), I’m getting MathJax [Math Processing Error]s when I try to use MathJax renderers SVG or Common HTML. Html-CSS is ok. A minimal reproduction for me is simply create a new notebook with a single markdown cell containing $x$, and right-click and use the menus to change renderers.

I see this in both lab and classic notebook, and I get it in both firefox and chrome (mac, big sur). The specific errors look like:

Error: a.FONTDATA is undefined

file: http://localhost:8888/static/components/MathJax/jax/output/SVG/jax.js?V=2.7.9
line: 19

Debugging tips: use 'unpacked/MathJax.js', inspect 'MathJax.Hub.lastError' in the browser console

Can anyone provide any suggestions for what is going on or how to resolve this? I’ve had no luck googling this, except that lots of results come up from the time back in the day when jupyter came with a stripped down version of MathJax that simply did not provide all the renderers, and similar symptoms occurred. (Definitely caused me much grief back then too!) But I thought this was changed a long time ago.

Edit: additional question, should I just post this as an issue, and if so, in what repository? (notebook?)

Bump – anyone have any ideas about this, or even where to start looking or where else to ask?