Try to add this snippet as mu-plugin (may also work in your functions.php file of your child theme):
add_action( 'after_setup_theme', function() {
add_theme_support( 'title-tag' );
remove_all_filters( 'wp_title' );
remove_all_filters( 'wpseo_title' );
remove_all_actions('wp_head', 'theme_slug_render_title');
add_filter( 'wp_title', 'sp_remove_title', 9999999999999, 2 );
}, 99999999999999);
function sp_remove_title( $title, $sep ) {
return false;
}
add_action('wp_loaded', 'buffer_start');
function buffer_start() {
ob_start("sp_remove_empty_title");
}
function sp_remove_empty_title($buffer) {
$buffer = str_replace('<title></title>','',$buffer);
return $buffer;
}