So initially I had dhcpd manually configured but did not specify it in the subnet configuration. This worked fine and I could provision systems without a problem and pxe requested the proper config from pxelinux.cfg/01-{MAC}.

However once I set the proxy for the dhcp server in the subnet config the pxe process suddenly stopped working.
The weird thing is that suddenly pxe tried the config from pxelinux.cfg/{sys-uuid}. There it simply got stuck.

The leases file contained this entry for the host:

host testsys.vms.local {
dynamic;
hardware ethernet 52:54:00:28:11:63;
fixed-address 10.100.0.124;
supersede server.filename = "pxelinux.0";
supersede server.next-server = 0a:63:00:28;
supersede host-name = "testsys.vms.local";
}

The moment I remove that entry and restart dhcpd pxe starts using the MAC address again and the pxe boot and the provisioning succeeds.