Twitter action items display “h”, “J” and “R” letters instead

This is a duplicate of https://wordpress.org/support/topic/twitter-actions-icons-are-gone-replaced-with-h-j-r/ but that issue appears not to have been properly resolved.

Action icons are replaced by “h”, “J” and “R”.

According to the other thread, this is caused by anchor tags being set to a font family which was blocking the plugin’s icons. But I would prefer not to have to change anything on the theme, and the plugin should handle this gracefully.