I re-installed my Guix System based on the ISO found here: https://ci.guix.gnu.org/build/175632/details
That's '/gnu/store/lw1j4gn8h51cbfp9dg0g025ngkg83sw1-image.iso.drv'. It's a simple system, but the process worked for me. It successfully recognized and re-used my existing /home partition. No trouble with the laptop's ethernet connection, and no trouble with missing substitutes or failing substitution.
