[_ck_]

Something I just realized and I should have noticed / asked sooner.

You are using a custom template. A very common problem with plugins when you use custom templates is they have accidentally removed some critical actions / filters.

Open up your register.php template and open up the original bb-templates/kakumei/register.php template.

Compare the two, specifically looking for any do_action or apply_filter that you are missing.

In your case, specifically

<?php do_action('extra_profile_info', $user); ?>

but I suspect you have that, or you’d see nothing from the plugin.