"The update information is outdated" warning won't go away. No information given about how to fix

[teo1978]

Starting today or yesterday, this warning (see screenshot) appears in the indicator area. It persists across reboot.

At the end it says "Please update manually by selecting 'Show updates' from the indicator menu, and watching for any failing repositories".

1) Doing what it says, that is, selecting "Show updates" only bring up the popup that says "The software on this computer is up to date"

2) How am I supposed to "watch for any failing repositories"?

So, the information given is confusing and utterly insufficient. It gives no clue about the real source of the problem, how to fix it, and it gives vague ("may be caused by this or that") and plain false ("please update manually...") information about how to even figure out what the source of the problem is.

Why doesn't it check automatically for "any failing repositories" and tell me which ones they are, what kind of "failure" it is and what I am supposed to do about it?

I remember the same thing happening ages ago, the warning stayed there for months, and I don't even know what I did to get rid of it.

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: update-manager 1:15.10.3
ProcVersionSignature: Ubuntu 4.2.0-30.36-generic 4.2.8-ckt3
Uname: Linux 4.2.0-30-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.19.1-0ubuntu5
Aptdaemon:

Architecture: amd64
CurrentDesktop: Unity
Date: Tue Mar 15 00:06:24 2016
GsettingsChanges:
 b'com.ubuntu.update-manager' b'show-details' b'true'
 b'com.ubuntu.update-manager' b'window-height' b'716'
 b'com.ubuntu.update-manager' b'first-run' b'false'
 b'com.ubuntu.update-manager' b'window-width' b'997'
 b'com.ubuntu.update-manager' b'launch-time' b'1457996685'
InstallationDate: Installed on 2013-10-11 (885 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release amd64 (20130424)
PackageArchitecture: all
SourcePackage: update-manager
UpgradeStatus: Upgraded to wily on 2016-01-18 (56 days ago)

[Launchpad Janitor (janitor)]

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

[Koen Roggemans (koen-roggemans)]

I see this same behaviour regularly on systems running 18.04 as well.
Running sudo apt update makes the update process resume - no errors shown.

Without doing that the system reports that it is up to date and it isn't, making it unsafe.

Non techy users freak out on using a command line command. I think this could and should be self healing, eg by running an apt update on resume after network up.