Hi @phil.owen
Thanks for the follow up. I believe the entire issue is that you are using acf_form within another form. This explains why the acf_form_head function is not running correctly.
Where does your custom form post to? Does it re-direct the page?
The acf_form_head function expects no redirection, and for the $_POST data to exist at the time it is called (at the top of the template file).
Does this help?
Thanks
E
