Your problem is that you can not use wp_title() in the theme if the theme already supports title-tag. The <head> of your theme should look like this:
<head>
<meta charset="<?php bloginfo( 'charset' ); ?>">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<?php wp_head(); ?>
</head>
The filter and title-tag support:
add_action( 'after_setup_theme', 'theme_functions' );
function theme_functions() {
add_theme_support( 'title-tag' );
}
add_filter( 'wp_title', 'custom_titles', 10, 2 );
function custom_titles( $title, $sep ) {
//Check if custom titles are enabled from your option framework
if ( ot_get_option( 'enable_custom_titles' ) === 'on' ) {
//Some silly example
$title = "Some other title" . $title;;
}
return $title;
}
If you do this, it will work perfectly.