I recently encountered what is likely the same bug. The directory /var/lib/gdm
had the correct permissions gdm:gdm, but all the files inside had something like
973:gdm

a43e9157ef479e94c19951cc9d228cf153bf78ee is supposed to fix this (duplicate bug
37423) but it only checks the permissions of /var/lib/gdm/ itself. Not all of
the files in it. This explains why in my case it failed to fix the permissions,
because the directory was gdm:gdm. How it got that way I don't know, and infact

it doesn't really matter. The directory is mutable, and thus can theoretically be

changed for any number of reasons. Therefore if we wish for Guix to be robust

with it's Functional design, and have meaningful rollbacks, we perhaps have no

choice but to assert the required invariants like these on mutable files.

A better solution may be to make it fully chown -R on reconfigure, but not each time

on boot?

I've attached an untested patch with a suggested solution of making
%gdm-activation operate every single time, instead of just after checking
/var/lib/gdm.