18.04 LTS to 20.04 LTS 'update-manager -c -d' OR 'do-release-upgrade -d' Fails >>no joy "transient"<<

[rb.eng]

Multiple attempts using 'update-manager -c -d' fail to work.
Have examined logs and failures seem to be related to "Broken" and "Try..." attempts. Multiple failures may be causing but it is unclear as error is convoluted.

For example apt.log

...
Investigating (0) libedata-cal-1.2-28:amd64 < 3.28.5-0ubuntu0.18.04.2 @ii mK Ib >
Broken libedata-cal-1.2-28:amd64 Depends on libebackend-1.2-10:amd64 < 3.28.5-0ubuntu0.18.04.2 -> 3.36.1-2 @ii umU > (= 3.28.5-0ub
  Considering libebackend-1.2-10:amd64 9 as a solution to libedata-cal-1.2-28:amd64 -2
  Removing libedata-cal-1.2-28:amd64 rather than change libebackend-1.2-10:amd64
  MarkDelete libedata-cal-1.2-28:amd64 < 3.28.5-0ubuntu0.18.04.2 @ii mK Ib > FU=0
 Try to Re-Instate (1) python-six:amd64
  MarkKeep python-six:amd64 < 1.11.0-2 -> 1.14.0-2 @ii umU Ib > FU=0
 Try to Re-Instate (1) python-pkg-resources:amd64
  MarkKeep python-pkg-resources:amd64 < 39.0.1-2 -> 44.0.0-2 @ii umU Ib > FU=0
 Try to Re-Instate (1) python-pyasn1:amd64
  MarkKeep python-pyasn1:amd64 < 0.4.2-3 -> 0.4.2-3build1 @ii ugU Ib > FU=0
 Try to Re-Instate (1) python-enum34:amd64
  MarkKeep python-enum34:amd64 < 1.1.6-2 -> 1.1.6-2ubuntu1 @ii ugU Ib > FU=0
 Try to Re-Instate (1) python-chardet:amd64
  MarkKeep python-chardet:amd64 < 3.0.4-1 -> 3.0.4-4build1 @ii umU Ib > FU=0
 Try to Re-Instate (1) python-html5lib:amd64
  MarkKeep python-html5lib:amd64 < 0.999999999-1 -> 1.0.1-2 @ii umU Ib > FU=0
 Try to Re-Instate (1) python-attr:amd64
  MarkKeep python-attr:amd64 < 17.4.0-2 -> 19.3.0-2 @ii ugU Ib > FU=0
 Try to Re-Instate (1) python-idna:amd64
  MarkKeep python-idna:amd64 < 2.6-1 -> 2.8-1 @ii ugU Ib > FU=0
 Try to Re-Instate (1) python-cryptography:amd64
  MarkKeep python-cryptography:amd64 < 2.1.4-1ubuntu1.3 -> 2.8-3 @ii ugU Ib > FU=0
 Try to Re-Instate (1) python-lxml:amd64
  MarkKeep python-lxml:amd64 < 4.2.1-1ubuntu0.1 -> 4.5.0-1 @ii umU Ib > FU=0
 Try to Re-Instate (1) python-decorator:amd64
  MarkKeep python-decorator:amd64 < 4.1.2-1 -> 4.4.2-0ubuntu1 @ii ugU Ib > FU=0
 Try to Re-Instate (1) python-numpy:amd64
  MarkKeep python-numpy:amd64 < 1:1.13.3-2ubuntu1 -> 1:1.16.5-2ubuntu7 @ii umU Ib > FU=0
 Try to Re-Instate (1) python-webencodings:amd64
  MarkKeep python-webencodings:amd64 < 0.5-2 -> 0.5.1-1ubuntu1 @ii umU Ib > FU=0
 Try to Re-Instate (1) python-bs4:amd64
  MarkKeep python-bs4:amd64 < 4.6.0-1 -> 4.8.2-1 @ii umU Ib > FU=0
 Try to Re-Instate (1) python-scandir:amd64
  MarkKeep python-scandir:amd64 < 1.7-1 -> 1.10.0-2ubuntu3 @ii ugU Ib > FU=0
 Try to Re-Instate (1) python-ipaddress:amd64
  MarkKeep python-ipaddress:amd64 < 1.0.17-1 -> 1.0.17-1build1 @ii ugU Ib > FU=0
 Try to Re-Instate (1) python-olefile:amd64
  MarkKeep python-olefile:amd64 < 0.45.1-1 -> 0.46-2 @ii umU Ib > FU=0
 Try to Re-Instate (1) python-pyasn1-modules:amd64
  MarkKeep python-pyasn1-modules:amd64 < 0.2.1-0.2 -> 0.2.1-0.2build1 @ii ugU Ib > FU=0
 Try to Re-Instate (1) python-pygments:amd64
  MarkKeep python-pygments:amd64 < 2.2.0+dfsg-1 -> 2.3.1+dfsg-1ubuntu2 @ii ugU Ib > FU=0
 Try to Re-Instate (1) python-dateutil:amd64
  MarkKeep python-dateutil:amd64 < 2.6.1-1 -> 2.7.3-3ubuntu1 @ii umU Ib > FU=0
 Try to Re-Instate (1) python-pil:amd64
  MarkKeep python-pil:amd64 < 5.1.0-1ubuntu0.2 -> 6.2.1-3 @ii umU Ib > FU=0
 Try to Re-Instate (1) python-pathlib2:amd64
  MarkKeep python-pathlib2:amd64 < 2.3.0-1 -> 2.3.5-1ubuntu1 @ii ugU Ib > FU=0
 Try to Re-Instate (1) python-backports.functools-lru-cache:amd64
  MarkKeep python-backports.functools-lru-cache:amd64 < 1.4-2 -> 1.5-3build1 @ii umU Ib > FU=0
 Try to Re-Instate (1) python-ptyprocess:amd64
  MarkKeep python-ptyprocess:amd64 < 0.5.2-1 -> 0.6.0-1ubuntu1 @ii ugU Ib > FU=0
 Try to Re-Instate (1) python-ipython-genutils:amd64
  MarkKeep python-ipython-genutils:amd64 < 0.2.0-1 -> 0.2.0-1ubuntu1 @ii ugU Ib > FU=0
 Try to Re-Instate (1) python-constantly:amd64
  MarkKeep python-constantly:amd64 < 15.1.0-1 -> 15.1.0-1build1 @ii ugU Ib > FU=0
 Try to Re-Instate (1) python-concurrent.futures:amd64
  MarkKeep python-concurrent.futures:amd64 < 3.2.0-1 -> 3.3.0-4 @ii ugU Ib > FU=0
 Try to Re-Instate (1) python-hyperlink:amd64
  MarkKeep python-hyperlink:amd64 < 17.3.1-2 -> 19.0.0-1 @ii ugU Ib > FU=0
 Try to Re-Instate (1) python-pam:amd64
  MarkKeep python-pam:amd64 < 0.4.2-13.2ubuntu4 -> 0.4.2-13.2ubuntu8 @ii ugU Ib > FU=0
 Try to Re-Instate (1) python-automat:amd64
  MarkKeep python-automat:amd64 < 0.6.0-1 -> 0.8.0-1ubuntu1 @ii ugU Ib > FU=0
 Try to Re-Instate (1) python-backports-abc:amd64
  MarkKeep python-backports-abc:amd64 < 0.5-2 -> 0.5-2ubuntu1 @ii ugU Ib > FU=0
 Try to Re-Instate (1) python-tk:amd64
  MarkKeep python-tk:amd64 < 2.7.17-1~18.04 -> 2.7.18-1 @ii umU Ib > FU=0
 Try to Re-Instate (1) python-singledispatch:amd64
  MarkKeep python-singledispatch:amd64 < 3.4.0.3-2 -> 3.4.0.3-2build1 @ii ugU Ib > FU=0

The final error is non-specific, suggesting it is "...most likely a transient problem"

Upgrading from Ubuntu 18.04.4 LTS

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.37
ProcVersionSignature: Ubuntu 4.15.0-99.100-generic 4.15.18
Uname: Linux 4.15.0-99-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.9-0ubuntu7.14
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: GNOME
Date: Sat May 2 19:53:01 2020
InstallationDate: Installed on 2018-05-08 (725 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
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 2020-05-02 (0 days ago)