@agowa338 I've seen this happen a time or two when upgrading the system, but for stuff like Firefox. I run the unstable channel, so this does happen sometimes.

Do you use configuration.nix or a flake?

If it's the former, I'd expect that the upstream channel had an update for a package, and that package wasn't cached, so you had to build it locally, but the update was bad, so the build failed.

If you use a flake, you can have the same thing happen after a 'nix flake upgrade' and make all of your packages repin to the newest version.

Sometimes you rebuild at juuust the wrong time and catch a package from nixpks in a broken state that is in the process of being patched.

There is a zero build failures campaign on right now to clean up the nixpkgs code base in preparation for the 25.11 release, so people are actively making lots of changes to the code.