[Bug 1907929] [NEW] Upgrade from 18.04 to 20.04 fails with "pkgProblemResolver::Resolve generated breaks, this may be caused by held packages"

[Brain]

Public bug reported:

$ lsb_release -rd
Description:	Ubuntu 18.04.5 LTS
Release:	18.04

-----------
$ do-release-upgrade -d

<snip>
Checking package manager
Reading package lists... Done    
Building dependency tree          
Reading state information... Done

Calculating the changes

Calculating the changes

Could not calculate the upgrade

An unresolvable problem occurred while calculating the upgrade.

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. 

<snip>
------

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.41
ProcVersionSignature: Ubuntu 4.15.0-128.131-generic 4.15.18
Uname: Linux 4.15.0-128-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.21
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Sun Dec 13 00:22:39 2020
InstallationDate: Installed on 2015-05-26 (2027 days ago)
InstallationMedia: Kubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2020-12-12 (0 days ago)

** Affects: ubuntu-release-upgrader (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug bionic dist-upgrade

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https://bugs.launchpad.net/bugs/1907929

Title:
  Upgrade from 18.04 to 20.04 fails with "pkgProblemResolver::Resolve
  generated breaks, this may be caused by held packages"

Status in ubuntu-release-upgrader package in Ubuntu:
  New

Bug description:
  $ lsb_release -rd
  Description:	Ubuntu 18.04.5 LTS
  Release:	18.04

  -----------
  $ do-release-upgrade -d

  <snip>
  Checking package manager
  Reading package lists... Done    
  Building dependency tree          
  Reading state information... Done

  Calculating the changes

  Calculating the changes

  Could not calculate the upgrade

  An unresolvable problem occurred while calculating the upgrade.

  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. 

  <snip>
  ------

  ProblemType: Bug
  DistroRelease: Ubuntu 18.04
  Package: ubuntu-release-upgrader-core 1:18.04.41
  ProcVersionSignature: Ubuntu 4.15.0-128.131-generic 4.15.18
  Uname: Linux 4.15.0-128-generic x86_64
  ApportVersion: 2.20.9-0ubuntu7.21
  Architecture: amd64
  CrashDB: ubuntu
  CurrentDesktop: ubuntu:GNOME
  Date: Sun Dec 13 00:22:39 2020
  InstallationDate: Installed on 2015-05-26 (2027 days ago)
  InstallationMedia: Kubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
  PackageArchitecture: all
  SourcePackage: ubuntu-release-upgrader
  UpgradeStatus: Upgraded to bionic on 2020-12-12 (0 days ago)

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