Enable systemd-networkd debugging

mkdir -p /etc/systemd/system/systemd-networkd.service.d/
Create Drop-In /etc/systemd/system/systemd-networkd.service.d/10-debug.conf with following content:

[Service]
Environment=SYSTEMD_LOG_LEVEL=debug
And restart systemd-networkd service:

systemctl daemon-reload
systemctl restart systemd-networkd
journalctl -b -u systemd-networkd