Can't incorporate "aarch64-sd-aarch64" image for existing system

Hey, today I tried to add a SD card image (nixos-generators) for an existing system (Raspberry Pi 3B+) to my snowfall-lib flake.

After creating the subfolders (systems/aarch64-sd-aarch64/system-name) I noticed that the normal nixosConfiguration for this system vanished, somehow, and so I couldn't use nixos-rebuild as usual (to remote x-compiling on x86_46 for aarch64 and deploy). But at the same state I could build the sd-aarch64Configurations (for this system).

FYI: I redacted some parts with […] (and changed the system name to system-name).

Before

[builder@x86_64:~]$ ls --tree -D systems/
systems
├── aarch64-linux
│  └── system-name
└── x86_64-linux
   └── […]

[builder@x86_64:~]$ nixos-rebuild build -v --option eval-cache false --use-remote-sudo --flake .#system-name --target-host system-name --use-substitutes
building the system configuration...
Building in flake mode.
$ nix --extra-experimental-features nix-command flakes build .#nixosConfigurations."system-name".config.system.build.toplevel -v --option eval-cache false --out-link /tmp/nixos-rebuild.IZmHN4/result
these 10 derivations will be built:
[…]

[builder@x86_64:~]$ nix flake show --all-systems --impure .
path:[…]
├───darwinModules: unknown
├───homeModules: unknown
├───lib: unknown
├───nixosConfigurations
│   ├───system-name: NixOS configuration
│   └───[…]
├───nixosModules
│   └───[…]
├───overlays
│   └───default: Nixpkgs overlay
├───pkgs: unknown
├───sd-aarch64Configurations: unknown
├───snowfall: unknown
└───templates

[builder@x86_64:~]$ nix -v build .#sd-aarch64Configurations.system-name
error: flake 'path:[…]' does not provide attribute 'packages.x86_64-linux.sd-aarch64Configurations.system-name', 'legacyPackages.x86_64-linux.sd-aarch64Configurations.system-name' or 'sd-aarch64Configurations.system-name'

Here everything is fine (and the last error is okay, because there still is no SD card image, it's just for illustration).

After

[builder@x86_64:~]$ ls --tree -D systems/
systems
├── aarch64-linux
│  └── system-name
├── aarch64-sd-aarch64
│  └── system-name
└── x86_64-linux
   └── […]

$ nix -v build .#sd-aarch64Configurations.system-name
these 6 derivations will be built:
[…]

[builder@x86_64:~]$ nix flake show --all-systems --impure .
path:[…]
├───darwinModules: unknown
├───homeModules: unknown
├───lib: unknown
├───nixosConfigurations
│   └───[…]
├───nixosModules
│   └───[…]
├───overlays
│   └───default: Nixpkgs overlay
├───pkgs: unknown
├───sd-aarch64Configurations: unknown
├───snowfall: unknown
└───templates

[builder@x86_64:~]$ nixos-rebuild build -v --option eval-cache false --use-remote-sudo --flake .#system-name --target-host system-name --use-substitutes
building the system configuration...
Building in flake mode.
$ nix --extra-experimental-features nix-command flakes build .#nixosConfigurations."system-name".config.system.build.toplevel -v --option eval-cache false --out-link /tmp/nixos-rebuild.7dFwHL/result
error: flake 'path:[…]' does not provide attribute 'packages.x86_64-linux.nixosConfigurations."system-name".config.system.build.toplevel', 'legacyPackages.x86_64-linux.nixosConfigurations."system-name".config.system.build.toplevel' or 'nixosConfigurations."system-name".config.system.build.toplevel'

As you can see here, the new SD image is building, but at nix flake show the nixosConfigurations > system-name is missing (and I get the error at nixos-rebuild).

May someone have a look? (I don't know if my relative simple flake is the problem, or if it's a problem with snowflake.)

Thanks a lot in advance and KR

BTW/FYI: At the end I currently have the goal to switch my running RPi3 system to disko. ATM it runs fine and I can nixos-rebuild, but I don't know how to deploy. So a SD image seemed a possible step, also if I wanna have this functionality in any case/later on …

Reproduce the issue with systems/aarch64-linux/system-name and systems/aarch64-sd-aarch64/system-name, then inspect the generated flake outputs with nix flake show --all-systems --impure. Compare the nixosConfigurations and sd-aarch64Configurations entries and verify both the nixos-rebuild and SD-image build commands work for the same system.