I tested this again today with Ubuntu 16.04, Xenial, but I installed the 16.10 version of unattended-upgrades and installed the version of systemd from xenial-updates before running the test. The results were the same and /var/log/unattended-upgrades/unattended-upgrades-shutdown.log is still empty.
I tested this again today with Ubuntu 16.04, Xenial, but I installed the 16.10 version of unattended-upgrades and installed the version of systemd from xenial-updates before running the test. The results were the same and /var/log/ unattended- upgrades/ unattended- upgrades- shutdown. log is still empty.