I am watching this bug on Lenovo G50-30 (CPU 2.1 GHz, 2Gb Ram):

# guix pull  --substitute-urls=https://berlin.guixsd.org
Updating channel 'guix' from Git repository at 'https://git.savannah.gnu.org/git/guix.git'...
Building from this channel:
  guix      https://git.savannah.gnu.org/git/guix.git    3995e85
Computing Guix derivation for 'x86_64-linux'... \
nothing to be done

# guix package  --substitute-urls=https://berlin.guixsd.org -u
substitute: updating substitutes from 'https://berlin.guixsd.org'... 100.0%
substitute: updating substitutes from 'https://berlin.guixsd.org'... 100.0%
building /gnu/store/6c4g38n9fhvnlk2vasn34mdd6nvpgx8m-python-minimal-3.6.5.drv...
/Killed
#

Python-minimal cannot compile.