hostname -f fails under reprotest

I'm debugging a weird reproducibility failure: lmod's testsuite fails during the second build performed by reprotest.

The package has no debian/salsa-ci.yml but uses the default from the pipeline repository.

After adding some debug statements I noticed that hostname -f errors out during the second build performed by reprotest.

First build: https://salsa.debian.org/hpc-team/lmod/-/jobs/6450080#L1845

hostname
runner-f0fdd533-project-66811-concurrent-0
hostname -f
runner-f0fdd533-project-66811-concurrent-0
domainname
(none)

Second build: https://salsa.debian.org/hpc-team/lmod/-/jobs/6450080#L4115

hostname
reprotest-capture-hostname
hostname -f
hostname: Name or service not known
make[1]: *** [debian/rules:32 : override_dh_auto_test] Erreur 1

I also tried the atomic reprotest, but all of them fail with the same error ...

E.g. the ASLR test reports https://salsa.debian.org/hpc-team/lmod/-/jobs/6450184#L3510

INFO:reprotest:build "experiment-1": FIX environment, FIX build_path, FIX kernel, vary aslr, FIX num_cpus, FIX time, vary user_group, FIX fileordering, vary domain_host, FIX home, FIX locales, FIX exec_path, FIX timezone, FIX umask

Why are user_group and domain_host always enabled during the atomic reprotest?

I also noticed that the UID of the user performing the second build is the same as that of the first build.