After installing a WordPress security plugin call All-In-One WP Security, MathJax failed to load some JS including.
- In the setting of the plugin, choose the tab Additional Firewall Rules
- Uncheck the option at the bottom, i.e. Advanced Character String Filter
- WordPress 5.3
- All In One WP Security v4.4.2
- MathJax-LaTex v1.3.11