Admin panel search doesn’t work for a specific custom post type

When I register multiple custom post types on the init hook, I don’t use multiple add_action functions. Consider this:

function m_register_custom_posts() {
 register_bolumpost();
 register_mangapost();
}
add_action('init','m_register_custom_posts');

I would also add all your custom taxonomy function calls into this function since they fire on the same init hook. You have a lot of custom functions firing on the init hook and you are not specifying a priority to fire the them. This can lead to problems. By putting all your custom functions that fire on the init hook into a single function, you control the order that the custom functions are firing.

It looks like you’ve got a filter set in line 91 that restricts your queries.

add_filter( 'pre_get_posts', 'tgm_io_cpt_search' );
function tgm_io_cpt_search( $query ) {

if ( $query->is_search ) {
$query->set( 'post_type', array( 'manga') );
}

return $query;

}

Try removing that filter and see what happens.