Until very recently having wrong permission on one of the networkd config files would result in networkd ignoring the rest of the perfectly readable network configuration files too, cutting off all network connectivity. (Systemd also requested the permission change iself.)

Currently there's a bug where if you have a bridge and all interfaces are disconnected from the bridge (I use hot-pluggable USB network interfaces) when you re-connect them, networkd will keep the bridge off. If you restart systemd-networkd it will fix itself.

I can name at least two instances already where I lost networking in my entire SBC farm, and had to pop out all microSD cards and fix the breakage manually, just because of systemd-networkd bugs. And I don't do anything crazy, just a single ethernet interface and two overlay wireguard networks, and mostly default config.

And fixing it yourself is not easy. I can do C coding perfectly fine, but I run 3 different CPU archs, so fixing it myself means compiling (3 times) and distributing my own systemd version to all my machines until upstream fixes the bug. It's not pleasant, nor easy.

I certainly understand people who miss having an ability to more readily script the system startup/network config.