If you are using Platform CDN and your SSL certificate is due to expire, you need to update the certificate both in the Acquia Cloud UI and on Platform CDN.
In the case that custom domains are using SSL certificate and Platform CDN, and you are updating the SSL on Acquia Cloud, it will not automatically be updated on Platform CDN. Please file a support ticket with Acquia Support, so that the Support team can update the certificate manually for Platform CDN.
Note - Please do not email your SSL certificate or attach your SSL certificate to a support ticket. Instead, if you must send a certificate to Acquia other than by using the Cloud Platform interface, contact Acquia Support, and we will advise you how to upload your SSL certificate and private key securely.