The PXE templates currently include the kickstart_kernel_options snippet, which does not work when both an IPv4 and v6 network is assigned to the host.
From what I can see there is a check for dual stack inside the snippet, which returns an error. I have adopted the template to work by preferring IPv4 over v6 in a PXE environment if both are configured at the host. I will create a pull request and would love feedback and corrections. Maybe it can be included in a future version.