Software Updater window "The software on this computer is up to date" appearing unexpectedly

[Bill Miller]

On several Ubuntu 20.04 computers after recent updates to the updating system (including updates to software-properties-gtk and its dependencies, the referenced Software Updater window is displayed after booting the PCs.

Unattended Updates are not enabled on the subject computers.

No manual run of update-manager was requested.

In this situation, receiving this pop up window is unexpected and unwelcome.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: update-manager 1:20.04.10.11 [modified: usr/lib/python3/dist-packages/UpdateManager/Dialogs.py]
ProcVersionSignature: Ubuntu 5.15.0-67.74~20.04.1-generic 5.15.85
Uname: Linux 5.15.0-67-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu27.25
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: MATE
Date: Sat Mar 4 08:00:53 2023
InstallationDate: Installed on 2018-04-27 (1771 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
PackageArchitecture: all
SourcePackage: update-manager
UpgradeStatus: Upgraded to focal on 2021-10-03 (517 days ago)