Separators disappeared after switching to Twenty Ten theme

I noticed after switching to the WordPress Twenty Ten theme (could have been before), that my separators were gone. In the linked page, the separator belongs after the phrase “I rest my case.”

I tried inserting a <hr /> custom HTML for the separator, and that <hr /> appears in the page HTML, but I assume somewhere it’s styled somehow to be invisible. I tried adding a “horizontal rule” element in the old visual editor, but it was invisible. I tried adding a “separator” with the block editor, but again, it was invisible.

I am not aware of any plug-in that alters text formatting. The ones I have are Akismet, Broken Link Checker (not active), Comet Cache, Hello Dolly (not active), Impostercide, Ninja Forms, Quote Comments, Ultimate Category Excluder, Use Google Libraries, Widgets on Pages, Wordfence Security, WP-Polls, XRDS-Simple.

Site is WordPress 6.2.2 and all plug-ins have auto-updates enabled.

I was switching from a commercial theme from Woo Commerce, Canvas, that broke with PHP 8.2. I have no idea what modifications have been made to that theme over the years to patch it up.

I need a global solution because the blog has over 4,000 articles.

The page I need help with: [log in to see the link]


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