I see this now:

#mv ~/.config/guix/latest{,.broken2}

# guix system reconfigure /etc/config.scm
guix system: warning: Consider running 'guix pull' followed by
'guix system reconfigure' to get up-to-date packages and security updates.

guix system: warning: /root/.config/guix/latest not found: 'guix pull' was never run
guix system: warning: Consider running 'guix pull' before 'reconfigure'.
guix system: warning: Failing to do that may downgrade your system!
substitute: updating list of substitutes from 'https://mirror.hydra.gnu.org'... substitute: updating list of substitutes from 'https://mirror.hydra.gnu.org'... 100.0%
substitute: updating list of substitutes from 'https://mirror.hydra.gnu.org'... substitute: updating list of substitutes from 'https://mirror.hydra.gnu.org'... substitute: updating list of substitutes from 'https://mirror.hydra.gnu.org'... substitute: updating list of substitutes from 'https://mirror.hydra.gnu.org'... substitute: updating list of substitutes from 'https://mirror.hydra.gnu.org'... 100.0%

Starting download of /gnu/store/a8vz60aiccnhzz35calv7wfzlgm2r312-linux-libre-4.16.4-gnu.tar.xz
From https://linux-libre.fsfla.org/pub/linux-libre/releases/4.16.4-gnu/linux-libre-4.16.4-gnu.tar.xz...
download failed "https://linux-libre.fsfla.org/pub/linux-libre/releases/4.16.4-gnu/linux-libre-4.16.4-gnu.tar.xz" 404 "Not Found"

Starting download of /gnu/store/a8vz60aiccnhzz35calv7wfzlgm2r312-linux-libre-4.16.4-gnu.tar.xz
From ftp://alpha.gnu.org/gnu/guix/mirror/linux-libre-4.16.4-gnu.tar.xz...
Throw to key `ftp-error' with args `(#<input-output: socket 14> "RETR linux-libre-4.16.4-gnu.tar.xz" 550 "Failed to open file.\r")'.

Starting download of /gnu/store/a8vz60aiccnhzz35calv7wfzlgm2r312-linux-libre-4.16.4-gnu.tar.xz
From https://ftpmirror.gnu.org/gnu/linux-libre/4.16.4-gnu/linux-libre-4.16.4-gnu.tar.xz...
following redirection to `https://mirror.tochlab.net/pub/gnu/linux-libre/4.16.4-gnu/linux-libre-4.16.4-gnu.tar.xz'...
download failed "https://mirror.tochlab.net/pub/gnu/linux-libre/4.16.4-gnu/linux-libre-4.16.4-gnu.tar.xz" 404 "Not Found"

Starting download of /gnu/store/a8vz60aiccnhzz35calv7wfzlgm2r312-linux-libre-4.16.4-gnu.tar.xz
From ftp://ftp.cs.tu-berlin.de/pub/gnu/linux-libre/4.16.4-gnu/linux-libre-4.16.4-gnu.tar.xz...
In procedure connect*: Connection timed out

Starting download of /gnu/store/a8vz60aiccnhzz35calv7wfzlgm2r312-linux-libre-4.16.4-gnu.tar.xz
From ftp://ftp.funet.fi/pub/mirrors/ftp.gnu.org/gnu/linux-libre/4.16.4-gnu/linux-libre-4.16.4-gnu.tar.xz...
Throw to key `ftp-error' with args `(#<input-output: socket 17> "CWD 4.16.4-gnu" 550 "Can't change directory to 4.16.4-gnu: No such file or directory\r")'.

Starting download of /gnu/store/a8vz60aiccnhzz35calv7wfzlgm2r312-linux-libre-4.16.4-gnu.tar.xz
From http://ftp.gnu.org/pub/gnu/linux-libre/4.16.4-gnu/linux-libre-4.16.4-gnu.tar.xz...
download failed "http://ftp.gnu.org/pub/gnu/linux-libre/4.16.4-gnu/linux-libre-4.16.4-gnu.tar.xz" 404 "Not Found"

Starting download of /gnu/store/a8vz60aiccnhzz35calv7wfzlgm2r312-linux-libre-4.16.4-gnu.tar.xz
From http://mirror.hydra.gnu.org/file/linux-libre-4.16.4-gnu.tar.xz/sha256/0lq3yv88yd9zcz52bl4hfllb41vy1i826gcim6qjjc88assqib9i...
download failed "http://mirror.hydra.gnu.org/file/linux-libre-4.16.4-gnu.tar.xz/sha256/0lq3yv88yd9zcz52bl4hfllb41vy1i826gcim6qjjc88assqib9i" 404 "Not Found"

Starting download of /gnu/store/a8vz60aiccnhzz35calv7wfzlgm2r312-linux-libre-4.16.4-gnu.tar.xz
From http://tarballs.nixos.org/sha256/0lq3yv88yd9zcz52bl4hfllb41vy1i826gcim6qjjc88assqib9i...
download failed "http://tarballs.nixos.org/sha256/0lq3yv88yd9zcz52bl4hfllb41vy1i826gcim6qjjc88assqib9i" 404 "Not Found"
failed to download "/gnu/store/a8vz60aiccnhzz35calv7wfzlgm2r312-linux-libre-4.16.4-gnu.tar.xz" from ("https://linux-libre.fsfla.org/pub/linux-libre/releases/4.16.4-gnu/linux-libre-4.16.4-gnu.tar.xz" "ftp://alpha.gnu.org/gnu/guix/mirror/linux-libre-4.16.4-gnu.tar.xz" "mirror://gnu/linux-libre/4.16.4-gnu/linux-libre-4.16.4-gnu.tar.xz")
builder for `/gnu/store/s3wzp8igh4g1x4fsp5l39gfia8q0bib6-linux-libre-4.16.4-gnu.tar.xz.drv' failed to produce output path `/gnu/store/a8vz60aiccnhzz35calv7wfzlgm2r312-linux-libre-4.16.4-gnu.tar.xz'
cannot build derivation `/gnu/store/pvfwji4aqr1764ylij8xabaqlx7qghn7-linux-libre-4.16.4-gnu.tar.xz.drv': 1 dependencies couldn't be built
cannot build derivation `/gnu/store/pvdzw7wk93ckhp0c8j7h2h3flgsf1mp8-linux-libre-4.16.4.drv': 1 dependencies couldn't be built
guix system: error: build failed: build of `/gnu/store/pvdzw7wk93ckhp0c8j7h2h3flgsf1mp8-linux-libre-4.16.4.drv' failed

What to do?