Gah – four pesky lines of code in the functions.php file.
//remove_filter( ‘the_content’, ‘nrelate_related_inject’, 10 );
//remove_filter( ‘the_excerpt’, ‘nrelate_related_inject’, 10 );
//add_filter( ‘the_content’, ‘nrelate_related_inject’, 99 );
//add_filter( ‘the_excerpt’, ‘nrelate_related_inject’, 99 );
Commented those out, and all my content is displaying correctly again.