Good news and bad news. The custom form appears to have a spambot trap, but it is obviously not working. So you need to contact MailChimp or whatever other plugin this is to ask them why the spambot trap is not working. Unfortunately, I don’t see anything that BPS can hook into for this custom sidebar form or any Bonus Custom Code that would be of any use for this type of custom sidebar form. And my guess is that the spambot trap is not working because it looks like you are caching or using a CDN for your home page. Kind of a double whammy there because you should never to cache a Form for any reason, but you do obviously want to cache your website home page. 😉 Check with MailChimp or whatever other plugin this is and see if there is a way to exclude just the custom form from being cached.
<!-- 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;" aria-hidden="true"><input type="text" name="b_f3a13f33378a894a0a7cec7a1_58b539bdf6" tabindex="-1" value=""></div>