Custom WP_List_Table displays blank rows
You’re getting the blank rows because your column headers are registered late. And you should register the headers (i.e. initialize the list table class instance) before admin notices are rendered on the page, i.e. before WordPress fires hooks like admin_notices. But your customer_list_page() function, which I believe, is a callback for either add_menu_page() or add_submenu_page(), … Read more