Not sure when you are trying to get the values. You cannot get acf field values until the ‘acf/init’ hook. You need to plan your code to get the value on or after this hook is fired.
to get the value
$value = get_field('field_name', 'user_'.$user_id);
https://www.advancedcustomfields.com/resources/how-to-get-values-from-a-user/
