It seems Cloud SQL Auth Proxy failed to set up proxy connections to the instance. It is likely because the language connectors/ auth proxy version is too old. Have you tried upgrading your Cloud SQL proxy version? If you are using Cloud SQL Auth Proxy, make sure you are using the most recent version, see keeping the Cloud SQL Auth Proxy up to date.

You can also check this documentation about Requirements for using the Cloud SQL Auth Proxy, it mentions connections to Cloud SQL instances using (shared/ customer-managed) Certificate Authority (CA) with the recommended Cloud SQL Auth Proxy version.

If upgrading the proxy version doesn't work for you and if you have a support package, I would recommend you getting help through reaching out to Google Cloud Support for a more in-depth analysis of your issue.