Due to a bug in Cliniko's MailChimp integration, when changing a patient's email address Cliniko added a new subscriber to MailChimp instead of updating the existing subscriber on the list. This caused duplicate patients in MailChimp, one with the old email address and one with the new address. This has now been fixed.
Unfortunately, due to the nature of this bug, you may need to manually clean your list within MailChimp or re-integrate into a new list. You can re-integrate by following Steps 12 onwards in our MailChimp integration article.