ToC (Table of Contents) Module output is broken

After adding the ToC module to a page and excluding everything but <h2> tags, the output looks fine. Save and publish, looks good. But on page reload, output breaks. Only the page title followed by a plus-sign and a minus-sign (hyphen) are rendered.

Page source shows an empty list, so the module is not generating the content. Nothing obvious in the console.

Page I need help with: National Social Justice Summit Program - TechBridge