In an Ubuntu 18.04 server, I was not able to rename network interfaces through proven config-management-applied systemd-networkd configuration working on all other servers.
The only difference I see between servers originally set-up by configuration management and this partially hand-petted machine is that the Ubuntu server has been upgraded from at least 14.04, maybe even 12.04.
Investigating initrd and comparing with a server that worked, two obvious differences appeared through upgrading Ubuntu:
/lib/udev/rules.d/71-biosdevname.rules
This is an old-times relict of renaming network interfaces in Ubuntu. It has to be deleted.
/etc/udev/rules.d/80-net-setup-link.rules
This was set-up shadowing /lib/udev/rules.d/80-net-setup-link.rules, which (among others) also applies configuration from systemd-networkd. It contains a message indicating some miss-interpreted setup as VM (actually, this is a bare metal server):
# This machine is most likely a virtualized guest, where the old persistent
# network interface mechanism (75-persistent-net-generator.rules) did not work.
# This file disables /lib/systemd/network/99-default.link to avoid
# changing network interface names on upgrade. Please read
# /usr/share/doc/udev/README.Debian.gz about how to migrate to the currently
# supported mechanism.
This file also has to be deleted.
A final update-initramfs -u && reboot results in properly renamed network interfaces.