Failure to create dualstack v6 primary cluster

[martinkennelly]

export IP_STACK=v6v4

# HOST_IP_STACK -
# IP stack for the host.
# Default: If unset, defaults to ${IP_STACK}.
# NOTE: arm64 does not support v6
# Choices: "v4", "v6", "v4v6"
#
export HOST_IP_STACK=v4v6

Not sure how to debug this further. It stalls when waiting for master:

level=debug msg=ironic_node_v1.openshift-master-host[0]: Still creating... [17m50s elapsed]

Install works fine with other configs.