I am using CMC - Mailchimp for Joomla version 4.1.2 on a site and it has a SSL certificate.
I also see mod_ccc_cmc_mailchimp version 1.3.1 and do not know what this is.
I got mixed content because one svg image is send over http:
http://domainname.nl/media/mod_cmc/images/loading-bubbles.svg
When I disable mod_ccc_cmc_mailchimp version 1.3.1 the http-error disappear. Is the mod_ccc_cmc_mailchimp version 1.3.1 an old version of the same extension? Then the solution is to remove this old version.