I've added some basic debugging of my own, and it seems it is caused by transitive_dependencies() function in /usr/bin/unattended-upgrade being called with pkg.name="systemd"
Note: I run sysvinit, and do not have "systemd" package installed. Are there any workarounds for using unattened-upgrade with sysvinit (eg. without systemd) in Buster? How about Bullseye? Thanks, Matija -- Opinions above are GNU-copylefted.
