It was disabled inc6953d1ff6because a recent Nixpkgs bump brought in a new systemd which changed how systemd-nspawn worked. As far as I can tell, the issue was caused by this upstream systemd commit:b71a0192c0Bind-mounting the host's `/sys` and `/proc` into the container's `/run/host/{sys,proc}` fixes the issue and allows the test to succeed.