There is a known issue that can occur when IP address conflicts are identified on the Provisioning network. As a consequence, discovery and/or deployment tasks will fail for hosts which are assigned an IP address which is already in use.
You can work around this issue by performing a port scan of the Provisioning network. Run from the Undercloud node, this will help validate whether the IP addresses used for the discovery and host IP ranges are available for allocation. You can perform this scan using the nmap utility. For example (replace the network with the subnet of the Provisioning network (in CIDR format)):
$ sudo yum install -y nmap
$ nmap -sn 192.0.2.0/24
As a result, if any of the IP addresses in use will conflict with the IP ranges in undercloud.conf, you will need to either change the IP ranges, or free up the IP addresses before running the introspection process, or deploying the Overcloud nodes.