App Runner not adding custom domain names to ACM certificate

We recently deployed a new App Runner service and added two custom domain names and setup the DNS records as required. Both domain names are now showing Status: Active.

When accessing the application using the App Runner provided URL everything works but when accessing via a custom domain we get a ERR_CERT_COMMON_NAME_INVALID error as the served certificate is only valid for *.<region>.awsapprunner.com.

Is there something we might be missing? It seems like a bug and that the AWS managed ELB is not adding the certificates to it's listeners or adding the additional CNs to the certificate.