With the latest form code update by MailChimp, there is a field added which helps lessen spam registrations. This code also affects HC to not functioning well with your MailChimp. 


A workaround would be to change the specific code, see below for the sample code fomr MailChimp (naked form) 


<!-- Begin MailChimp Signup Form -->

<div id="mc_embed_signup">

<form action="" method="post" id="mc-embedded-subscribe-form" name="mc-embedded-subscribe-form" class="validate" target="_blank" novalidate>

 

<div class="mc-field-group">

 <label for="mce-EMAIL">Email Address </label>

 <input type="email" value="" name="EMAIL" class="required email" id="mce-EMAIL">

</div>

 <div id="mce-responses" class="clear">

  <div class="response" id="mce-error-response" style="display:none"></div>

  <div class="response" id="mce-success-response" style="display:none"></div>

 </div> <!-- real people should not fill this in and expect good things - do not remove this or risk form bot signups-->

    <div style="position: absolute; left: -5000px;"><input type="text" name="b_ad2554925dfccd2592a9f3720_d4f00e3ee6" value=""></div>

 <div class="clear"><input type="submit" value="Subscribe" name="subscribe" id="mc-embedded-subscribe" class="button"></div>

</form>

</div>

<!--End mc_embed_signup-->


With that given, you have to look for (see below) the code and change the field type from "text" to"hidden", I have marked the text as bold


 <!-- real people should not fill this in and expect good things - do not remove this or risk form bot signups-->

    <div style="position: absolute; left: -5000px;"><input type="text" name="b_ad2554925dfccd2592a9f3720_d4f00e3ee6" value=""></div>


After changing this, your form should work now and will get new subscribers registered.


If you're still having the issue. send us a ticket in helpdesk so we can investigate.