You are loading custom.js before the Lightbox script.
Try adding extra dependencies to your enqueue
wp_enqueue_script('customjs', get_template_directory_uri() . '/js/nutrition_club_theme.js', array('jquery', 'jquery-portfoliolightbox', 'jquery-magnific-popup'), '4.8', false);
Or whatever the script adding the lightBox is. You should always make sure you set dependencies correctly to avoid this.
NOTE: you should also make sure that if there is an enqueued script ( like the lightBox one ) that requires jQuery, has it set as a dependency.