Obtained this error a few minutes ago while performing a guix pull. I'm
running a foreign installation of guix atop Ubuntu 18.04.

guix substitute: error: download from '
https://ci.guix.gnu.org/nar/gzip/mzfkrxd4w8vqrmyrx169wj8wyw7r8i37-bash'
failed: 502, "Bad Gateway"
@ substituter-failed /gnu/store/mzfkrxd4w8vqrmyrx169wj8wyw7r8i37-bash 256
fetching path `/gnu/store/mzfkrxd4w8vqrmyrx169wj8wyw7r8i37-bash' failed
with exit code 1
@ substituter-started
/gnu/store/xxv1sk5y2bzi08v13dzs8cmsnivqsf22-automake-1.16.1
/gnu/store/ncknl03pkmamrxg7q9nxi1rn1qhvwbi9-guix-1.0.1/libexec/guix/substitute
killing process 2973
Backtrace:
In ice-9/eval.scm:
    159:9 19 (_ #(#(#(#(#(#(#(#(#(#(#(#(#(#<directory (guile-user)
7fdaa56861?> ?) ?) ?) ?) ?) ?) ?) ?) ?) ?) ?) ?) ?))
In ./guix/store.scm:
  1848:24 18 (run-with-store #<store-connection 256.99 7fdaa42436c0> _
#:guile-for-build _ #:system _ #:target _)
   1701:8 17 (_ _)
In ./guix/gexp.scm:
    896:2 16 (_ _)
    757:2 15 (_ _)
In ./guix/monads.scm:
    482:9 14 (_ _)
In ./guix/gexp.scm:
   627:13 13 (_ _)
In ./guix/store.scm:
   1701:8 12 (_ _)
In ./guix/gexp.scm:
    896:2 11 (_ _)
    757:2 10 (_ _)
In ./guix/monads.scm:
    482:9  9 (_ _)
In ./guix/gexp.scm:
   627:13  8 (_ _)
In ./guix/store.scm:
   1701:8  7 (_ _)
   1701:8  6 (_ _)
  1736:38  5 (_ #<store-connection 256.99 7fdaa1790600>)
In ./guix/packages.scm:
   948:16  4 (cache! #<weak-table 471/883> #<package
guix-daemon@1.0.1-14.c2f9ea2 7fdaa1471e70> ("x86_64-linux" . #t) ?)
In ./guix/grafts.scm:
    323:4  3 (graft-derivation #<store-connection 256.99 7fdaa1790600>
#<derivation /gnu/store/wykwvbsvg32l6gp194w5?> ?)
    172:4  2 (references-oracle #<store-connection 256.99 7fdaa1790600>
#<<derivation-input> drv: #<derivation /gnu/?>)
   182:20  1 (_ _ _)
In ./guix/store.scm:
  1224:15  0 (_ #<store-connection 256.99 7fdaa1790600> _ _)

./guix/store.scm:1224:15: Throw to key `srfi-34' with args `(#<condition
&store-protocol-error [message: "some substitutes for the outputs of
derivation `/gnu/store/5n6x7adw570w43is1x6qakvh37v4bdqb-bash.drv' failed
(usually happens due to networking issues); try `--fallback' to build
derivation from source " status: 1] 7fda9a52e9c0>)'.
guix pull: error: You found a bug: the program
'/gnu/store/n5wgvz287dwm62474mr42x34wl5j5wh7-compute-guix-derivation'
failed to compute the derivation for Guix (version:
"3fd8d20e56e1199c124af6d1d6dc2bb2b56943ef"; system: "x86_64-linux";
host version: "b40f4052891886348b10164f304d1c848bb2eeea"; pull-version: 1).
Please report it by email to <bug-guix@gnu.org>.