Comment 1 for bug 1723761

There are two modes of running u-u chosen by setting Unattended-Upgrade::InstallOnShutdown to "false" (default) or "true".

When InstallOnShutdown is "false" apt's apt-daily-upgrade.service runs u-u thus this service needs to ensure that network is still up, to not break similar packages.

Note that while vast majority of packages do not need network connection during installation a small fraction of them do perform downloads thus apt's service should try to keep the network up.

When InstallOnShutdown is "true" unattended-upgrades.service is responsible for keeping the network connection up and I believe versions starting with 0.93.1+nmu1 are fixed.