Clicking "Show Updates" does not update manually as described

[Phill]

Update manager applet shows a warning message as follows:

"The update information is outdated. This may be caused by network problems or by a repository that is no longer available. Please update manually by selecting 'Show updates' from the indicator menu, and watching for any failing repositories."

However, clicking 'Show updates' does not reload anything.

Running 'Software Updater' separately downloads the updated repositories by does not remove the notification.

Installing the updates using 'Software Updater' removes the notification roughly at the point that downloads are completed, but this could just be a timing coincidence.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: update-manager 1:16.04.4
ProcVersionSignature: Ubuntu 4.4.0-51.72-generic 4.4.30
Uname: Linux 4.4.0-51-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.1
Aptdaemon:

Architecture: amd64
CurrentDesktop: Unity
Date: Thu Dec 8 10:26:56 2016
DpkgHistoryLog.txt:
 Start-Date: 2016-12-01 10:14:14
 Commandline: aptdaemon role='role-commit-packages' sender=':1.88'
 Install: linux-headers-4.4.0-51-generic:amd64 (4.4.0-51.72, automatic), linux-headers-4.4.0-51:amd64 (4.4.0-51.72, automatic), linux-image-4.4.0-51-generic:amd64 (4.4.0-51.72, automatic), linux-image-extra-4.4.0-51-generic:amd64 (4.4.0-51.72, automatic)
 Upgrade: linux-headers-generic:amd64 (4.4.0.47.50, 4.4.0.51.54), linux-libc-dev:amd64 (4.4.0-47.68, 4.4.0-51.72), linux-image-generic:amd64 (4.4.0.47.50, 4.4.0.51.54), linux-generic:amd64 (4.4.0.47.50, 4.4.0.51.54)
 End-Date: 2016-12-01 10:15:34
ExecutablePath: /usr/bin/update-manager
GsettingsChanges:
 b'com.ubuntu.update-manager' b'show-details' b'true'
 b'com.ubuntu.update-manager' b'window-height' b'705'
 b'com.ubuntu.update-manager' b'first-run' b'false'
 b'com.ubuntu.update-manager' b'window-width' b'753'
 b'com.ubuntu.update-manager' b'launch-time' b'1481192740'
InstallationDate: Installed on 2016-06-03 (187 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
InterpreterPath: /usr/bin/python3.5
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=en_GB:en
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: update-manager
UpgradeStatus: No upgrade log present (probably fresh install)