In section "Restricting the API server to private"[1] of doc "Configuring a private cluster"[1], it describes at 1.a:
"For Azure, delete the api-internal-v4 rule for the public load balancer."

1. On 4.17+, inbound rule name is changed from "api-internal-v4" to "api-v4" in public load balancer.
2. On 4.17+, more resources need to be deleted manually besides "api-internal-v4" rule.
* associated frontenIPConfiguration
* associated public IP


[1]:https://docs.openshift.com/container-platform/4.17/post_installation_configuration/configuring-private-cluster.html#private-clusters-setting-api-private_configuring-private-cluster                       

    1.
    2.
    3.