unattended-upgrades post-installation script returned error exit status 128 due to debconf passthrough frontend failing

[Hans]

package unattended-upgrades 0.90ubuntu0.1 failed to install/upgrade: subprocess installed post-installation script returned error exit status 128

ProblemType: Package
DistroRelease: Ubuntu 16.04
Package: unattended-upgrades 0.90ubuntu0.1
ProcVersionSignature: Ubuntu 4.4.0-45.66-generic 4.4.21
Uname: Linux 4.4.0-45-generic x86_64
.var.log.unattended-upgrades.unattended-upgrades.log:

ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
Date: Wed Nov 2 09:21:06 2016
ErrorMessage: subprocess installed post-installation script returned error exit status 128
InstallationDate: Installed on 2016-07-29 (95 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
PackageArchitecture: all
RelatedPackageVersions:
 dpkg 1.18.4ubuntu1.1
 apt 1.2.12~ubuntu16.04.1
SourcePackage: unattended-upgrades
Title: package unattended-upgrades 0.90ubuntu0.1 failed to install/upgrade: subprocess installed post-installation script returned error exit status 128
UpgradeStatus: No upgrade log present (probably fresh install)
modified.conffile..etc.apt.apt.conf.d.10periodic:
 APT::Periodic::Update-Package-Lists "1";
 APT::Periodic::Download-Upgradeable-Packages "1";
 APT::Periodic::AutocleanInterval "0";
 APT::Periodic::Unattended-Upgrade "0";
mtime.conffile..etc.apt.apt.conf.d.10periodic: 2016-09-14T10:24:20.453516

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.