This feature was working about a month ago. All of a sudden it is not. I just made MailChimp extension update too.
Form works and passes data in WordPress.
When MailChimp opt-in is checked, form passes data to WordPress but will not pass data to MailChimp.
When MailChimp opt-in is not checked, form passes data to WP and passes data to MailChimp. I then receive an email.
It will not send email to confirm subscription if opt-in is checked.