When running openshift-install agent create image, and the install-config.yaml does not contain platform baremetal settings (except for VIPs) warnings are still generated as below:
DEBUG         Loading Install Config...            
WARNING Platform.Baremetal.ClusterProvisioningIP: 172.22.0.3 is ignored 
DEBUG Platform.Baremetal.BootstrapProvisioningIP: 172.22.0.2 is ignored 
WARNING Platform.Baremetal.ExternalBridge: baremetal is ignored 
WARNING Platform.Baremetal.ExternalMACAddress: 52:54:00:12:e1:68 is ignored 
WARNING Platform.Baremetal.ProvisioningBridge: provisioning is ignored 
WARNING Platform.Baremetal.ProvisioningMACAddress: 52:54:00:82:91:8d is ignored 
WARNING Platform.Baremetal.ProvisioningNetworkCIDR: 172.22.0.0/24 is ignored 
WARNING Platform.Baremetal.ProvisioningDHCPRange: 172.22.0.10,172.22.0.254 is ignored 
WARNING Capabilities: %!!(MISSING)s(*types.Capabilities=<nil>) is ignored 

It looks like these fields are populated with values from libvirt as shown in .openshift_install_state.json:
            "platform": {
                "baremetal": {
                    "libvirtURI": "qemu:///system",
                    "clusterProvisioningIP": "172.22.0.3",
                    "bootstrapProvisioningIP": "172.22.0.2",
                    "externalBridge": "baremetal",
                    "externalMACAddress": "52:54:00:12:e1:68",
                    "provisioningNetwork": "Managed",
                    "provisioningBridge": "provisioning",
                    "provisioningMACAddress": "52:54:00:82:91:8d",
                    "provisioningNetworkInterface": "",
                    "provisioningNetworkCIDR": "172.22.0.0/24",
                    "provisioningDHCPRange": "172.22.0.10,172.22.0.254",
                    "hosts": null,
                    "apiVIPs": [
                        "10.1.101.7",
                        "2620:52:0:165::7"
                    ],
                    "ingressVIPs": [
                        "10.1.101.9",
                        "2620:52:0:165::9"
                    ]

The install-config.yaml used to generate this has the following snippet:
platform:
  baremetal:
    apiVIPs:
    - 10.1.101.7
    - 2620:52:0:165::7
    ingressVIPs:
    - 10.1.101.9
    - 2620:52:0:165::9
additionalTrustBundle: |

4.12.0

Happens every time

1. Use install-config.yaml with no platform baremetal fields except for the VIPs
2. run openshift-install agent create image 

Warning messages are output

No warning messags