Describe the bug

I set up my desktop computer as a build machine and binary cache for my laptop.
when I turn off my desktop, every build on my laptop fails.

I can't tell if it is because the desktop is a build machine, or because it's a binary cache, but in both cases this should not be happening.

Steps To Reproduce

1. Set up machine B as a build machine and binary cache for machine A
2. Turn off machine B
3. Run nix-build on machine A

Expected behavior

A builds everything itself.

nix-env --version output

$ nix-env --version
nix-env (Nix) 2.3.6