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Can you paste here the exact content from the text view of the content editor of that page.
After that @weaver may be of more help
It was with the Show/hide if mobile, and from the class on the body tag he appears to be running Smart No stack.
And here it is not that it does not work, but that initially you have The + AND text showing. If you click the + it changes to _ with text showing (which is normal, and if you click again then you have the + text not showing, After that it works fine.
The issue is that the initial state which text hidden is wrong, but only the initial state.