bug#54447: cuirass: missing derivation error

[Mathieu Othacehe]

Hello,

A lot of builds, among them ~20 system tests[1], are failing with:
"cannot build missing derivation
?/gnu/store/hs6kp1lqgymhyp3jndc0dsp0pn4psgv0-gui-installed-desktop-os-encrypted.drv?"
errors.

Those derivations are present on the CI head node. This means that the
errors occur during substitution. This is most likely caused by some
issue with the publish server, because:

- The publish server serves a 404 error. We should get rid once and for
  all of this 404 thing, pushing something like:
  https://issues.guix.gnu.org/50040.

or

- The publish server is not fast enough and hits an Nginx timeout that
  closes the communication.

Any other cause I could be missing?

Thanks,

Mathieu

[1]: https://ci.guix.gnu.org/eval/159975?status=failed