Ubuntu 18.04 AWS images - and probably other Cloud images as well - have automated upgrades turned on. This is done via two systemd timers, apt-daily.timer and apt-daily-upgrade.timer. The timers kick of periodically as well as when an instance is rebooted. This sounds reasonable until you are provisioning something: you’re unable to install or configure any packages while apt and/or dpkg are running. With a really fresh cloud base image this may not be an issue, but when the base image gets sufficiently old then apt-get upgrade starts taking enough time to cause issues.