when this hook fires save_post_ctp ACF has not yet saved data. This hook is fired before ACF saves anything. You need to use the acf/save_post hook or you need to use the WP “save_post” hook with a priority > 10.
If you want to get data before ACF has saved values then you need to look in $_POST['acf']
Welcome to the Advanced Custom Fields community forum.
Browse through ideas, snippets of code, questions and answers between fellow ACF users