I also found this in my functions.php file — not sure if it’s the issue:
/**
* Calls the Standard SEO Titles plugin during the wp_title action to render
* SEO-friendly page titles.
*/
if( standard_using_native_seo() ) {
function standard_seo_titles() {
include_once( get_template_directory() . '/lib/seotitles/standard_seotitles.php' );
echo Standard_SeoTitles::get_page_title( get_the_ID() );
} // end standard_seo_tiltes
add_filter( 'wp_title', 'standard_seo_titles' );
} // end if