MailChimp's default popup scripts can break on WordPress sites that use jQuery/jQuery UI unless you include their embed code as the final elements before the closing body tag.
Including them in this way isn't always possible or easy with WordPress.
The code below is an alternative implementation of the loader that forces MailChimp's popup scripts to appear below all other scripts upon page load.
To use it, modify the baseUrl, uuid, and lid attributes with the ones from the original popup script that MailChimp supplies.