ubuntu upgrade to 20 from 18 .04.5 fails. Error message is indeterminate.

[Todd Wermers]

Ubuntu 18.04.5 LTS
upgrading to latest LTS version.
Expecting the upgrade to proceed or at least give me a useful error, however it doesn't display an error. Instead it just states "Could not calculate the upgrade. An unresolvable problem occurred while calculating the upgrade. If none of this applies report the bug.
Since there is no problem listed with the error message, I would expect one to be listed. Since none of the error does apply (nothing listed) I'm reporting it as a bug.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.42
ProcVersionSignature: Ubuntu 4.15.0-140.144-generic 4.15.18
Uname: Linux 4.15.0-140-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia
ApportVersion: 2.20.9-0ubuntu7.23
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Thu Apr 8 13:50:31 2021
InstallationDate: Installed on 2017-10-13 (1273 days ago)
InstallationMedia: Ubuntu 16.04.3 LTS "Xenial Xerus" - Release amd64 (20170801)
PackageArchitecture: all
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2021-04-08 (0 days ago)
VarLogDistupgradeTermlog:

[Manfred Hampl (m-hampl)]

I assume that the message that you are missing should read

    This was likely caused by:
    Unofficial software packages not provided by Ubuntu
    Please use the tool 'ppa-purge' from the ppa-purge
    package to remove software from a Launchpad PPA and
    try the upgrade again.

This is the case on your system. You have added software from outside Ubuntu, namely the oibaf PPA.

[Todd Wermers (twtechmeister)]

I got past the issue by removing all the packages listed here for my distro. Upgrade is now commencing.
https://www.ubuntuupdates.org/ppa/xorg-edgers?dist=bionic&id=87&page=1

[Todd Wermers (twtechmeister)]

It would be useful if that message or something similar to what m-hample stated was displayed. It would also be useful to provide a link to the official repository names in the error.

[Launchpad Janitor (janitor)]

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