/etc/systemd/scripts/ is not a standard directory.
Run shellchek on the choose-mirror script.
archiso/mkarchiso
configs/{baseline,releng}/build.sh
configs/releng/airootfs/root/.automated_script.sh
+ configs/releng/airootfs/usr/local/bin/choose-mirror
[Service]
Type=oneshot
-ExecStart=/etc/systemd/scripts/choose-mirror
+ExecStart=/usr/local/bin/choose-mirror
[Install]
WantedBy=multi-user.target