Hello @Roy J.,
Welcome to the Klaviyo Community!
Using hidden fields in your signup form is a great way to collect more information about your subscribers! From my experience, this sort of behavior can happen if you forget to republish your form after making any edits or changes to your form. After making changes to a form, it’s imperative to publish the form again to have the edits reflected in the public version of the form on your site. This is also mentioned in the Publish a Form subsection of the How to Create and Manage Signup Forms Help Center articles:
When making edits to a form that is already live, you will have to publish the edits before they appear on your site. Once you make a change to a live form, it will automatically be saved. However, you will then see the option to publish changes beside the form's live status.
I hope this helps!
David
