Custom Post Type not visible on category page

Custom post types are excluded from the main query by default (except on taxonomy pages and custom post type archive pages), that is why you don’t see posts from your custom post type on your category page.

You need to include your custom post type posts in the main query manually. That is done with pre_get_posts which alters the main query before it is executed.

You can do the following to include your custom post type on category pages

function custom_post_type_cat_filter($query) {
  if ( !is_admin() && $query->is_main_query() ) {
    if ($query->is_category()) {
      $query->set( 'post_type', array( 'post', 'YOUR CPT' ) );
    }
  }
}

add_action('pre_get_posts','custom_post_type_cat_filter');