swebdev

That’s likely an issue with mathjax cdn, which is shut down, see https://www.mathjax.org/cdn-shutting-down/

The fix is to use the cdnjs mathjax cdn instead:
https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.5/MathJax.js

(go to settings for this plugin, and add the above cdn under “Custom MathJax location” field).

Worked for me.