It is the
apt-daily-upgrade.service called with the
apt-daily-upgrade.timer every day. I don't know why it make problems on your installation. Anyway, you don't want to run it automatically. You can disable the timer with:
rpi ~$ sudo systemctl disable apt-daily-upgrade.timer
The problem is that you can't do it because the boot get stuck on executing the service. When I look at the service with:
rpi ~$ systemctl cat apt-daily-upgrade.service
Description=Daily apt upgrade and clean activities
After=apt-daily.service network.target network-online.target systemd-networkd.service NetworkManager.service connman.service
I see that the service will timeout (TimeoutStopSec) after 900 seconds, that are 15 minutes. So boot your RasPi and wait at least 15 min. Maybe the RasPi will continue booting and you are able to disable the timer.
If you want to disable the timer before first booting you must mount the second ext4 root partition of the CD Card on a computer with a linux operating system. Other operating systems are not able to mount ext4. If you have mounted the root partition to e.g.
/mnt/ then you can disable the
apt-daily-upgrade.timer by deleting a symlink:
pc ~$ sudo rm /mnt/etc/systemd/system/timers.target.wants/apt-daily-upgrade.timer