@sam It turns out that KaTeX isn’t working quite right in the new plugin. If you take a look at it, it’s quite clearly a missing font problem and, indeed, the console indicates that there a bunch of font (Woff-v2) files that are not found.
The fonts actually exist in the correct location, which should be in a folder named ‘fonts’ adjacent to the style sheet. Both of these files exist on my development version, for example:
http://localhost:4200/plugins/discourse-math/katex/katex.min.css
and
http://localhost:4200/plugins/discourse-math/katex/fonts/KaTeX_Size2-Regular.woff2
When we take a look at the Network tab of the console, it appears that it’s trying to download something like
http://localhost:4200/t/my-topic/fonts/KaTeX_Size2-Regular.woff2
Thus, the browser is looking in a ‘fonts’ folder adjacent to the topic URL, which is clearly wrong.
I suppose this all has something to do with the loadKaTeX function defined in the katex-bundle, which I guess loads KaTeX in a non-standard way leading to KaTeX not really knowing where the CSS file lives. I don’t know how to fix it, though.