While working on reproducible builds for openSUSE, I found that
guile .go object files vary when created in parallel
e.g. with make -j3

This not only affected the guile package itself until
https://build.opensuse.org/request/show/732638

It also still affects our guix package.
But only that one seems to be left.

Building non-parallel means a slowdown of roughly 200-250%
so 2200-2600 seconds instead of 1100.

Not sure, if there is already a better upstream bug than
https://issues.guix.gnu.org/issue/20272

You could search for a better report there or file one.
I know several Guix devs stumbled over guile .go nondeterminism
and would like to see it fixed.