upgrade failed: could not calculate the upgrade (from fresh new/fully patched 18.04 LTS install)

[Daniel LaSalle]

Installed 18.04.4 LTS 2 weeks ago on a box I had left dormant since then.

1.
sudo apt update && sudo apt upgrade -y
= OK

2.
sudo update-manager -d
[...]
Could not calculate the upgrade

An unresolvable problem occurred while calculating the upgrade.

 This was caused by:
 * Upgrading to a pre-release version of Ubuntu
This is most likely a transient problem,
please try again later.
If none of this applies, then please report this bug using the command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal. If you want to investigate this yourself the log files in '/var/log/dist-upgrade' will contain details about the upgrade. Specifically, look at 'main.log' and 'apt.log'.

tried a 2nd time as suggested, same error.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.37
ProcVersionSignature: Ubuntu 5.3.0-51.44~18.04.2-generic 5.3.18
Uname: Linux 5.3.0-51-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.14
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: MATE
Date: Mon May 11 20:05:57 2020
InstallationDate: Installed on 2020-05-05 (6 days ago)
InstallationMedia: Ubuntu-MATE 18.04.4 LTS "Bionic Beaver" - Release amd64 (20200203.1)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2020-05-12 (0 days ago)
VarLogDistupgradeTermlog:

[Brian Murray (brian-murray)]

We've recently updated the release upgrader and it includes a change which may resolve the failure to calculate the release upgrade which you encountered. Please try the upgrade again and report back. Thanks in advance!

[Launchpad Janitor (janitor)]

[Expired for ubuntu-release-upgrader (Ubuntu) because there has been no activity for 60 days.]