Buttons don't show when "menu" is set for "single article". That is not a bug, it is intended to work this way, because joomla "single article" option exist to publish static pages, like home, front page, about us, copyrights, terms of use, etc., where social buttons do not make sense.
But it is easy to show buttons on any page. Just create a new category, last say "one article category". Then take the article you want to include the social buttons and associate to that category. On the menu for that page, choose "category blog" instead of single article, and choose "one article category". Now the static page will show the social buttons.
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