Several events led to this problem.
Notifications - Our notifications for admin, beta and production were set properly to notify support@cavo.io for unreachable instances as well as for certificate expiration.
Mail Server - Our mail server was set to properly forward these notifications to Intercom, our ticketing system.
Intercom - Intercom changed the target email address in charge of receiving emails forwarded to support@cavo.io. As such, our support team was not notified that the certificates were an issue.
*.cavo.io certificate - The new certificate was renewed last month.
*.apello.io certificate - This new “branding” certificate was obtained at the same time.
In order to minimize confusion, we implemented the apello.io certificate and failed to update the cavo.io certificate. This oversight coupled with the lack of notifications led to the issue.
Steps Taken to mitigate: