Here is the content of /var/log/dist-upgrade/main.log (file path may differ):

root@snoobeam:/# cat /var/log/dist-upgrade/main.log 
2020-05-28 21:03:34,995 INFO Using config files '['./DistUpgrade.cfg']'
2020-05-28 21:03:34,995 INFO uname information: 'Linux snoobeam.com 5.4.0-33-generic #37-Ubuntu SMP Thu May 21 12:53:59 UTC 2020 x86_64'
2020-05-28 21:03:35,113 INFO apt version: '1.9.4ubuntu0.1'
2020-05-28 21:03:35,113 INFO python version: '3.7.5 (default, Apr 19 2020, 20:18:17) 
[GCC 9.2.1 20191008]'
2020-05-28 21:03:35,114 INFO release-upgrader version '20.04.19' started
2020-05-28 21:03:35,129 INFO locale: 'en_US' 'UTF-8'
2020-05-28 21:03:35,202 INFO screen could not be run
2020-05-28 21:03:35,271 DEBUG Using 'DistUpgradeViewText' view
2020-05-28 21:03:35,337 DEBUG enable dpkg --force-overwrite
2020-05-28 21:03:35,436 DEBUG creating statefile: '/var/log/dist-upgrade/apt-clone_system_state.tar.gz'
2020-05-28 21:03:36,399 DEBUG lsb-release: 'eoan'
2020-05-28 21:03:36,400 DEBUG _pythonSymlinkCheck run
2020-05-28 21:03:36,402 DEBUG openCache()
2020-05-28 21:03:36,403 DEBUG quirks: running PreCacheOpen
2020-05-28 21:03:36,403 DEBUG running Quirks.PreCacheOpen
2020-05-28 21:03:36,671 DEBUG /openCache(), new cache size 10843
2020-05-28 21:03:36,672 DEBUG need_server_mode(): can not find a desktop meta package or key deps, running in server mode
2020-05-28 21:03:36,672 DEBUG checkViewDepends()
2020-05-28 21:03:36,678 DEBUG running doUpdate() (showErrors=False)
2020-05-28 21:03:37,783 DEBUG openCache()
2020-05-28 21:03:38,020 DEBUG /openCache(), new cache size 10843
2020-05-28 21:03:38,020 DEBUG doPostInitialUpdate
2020-05-28 21:03:38,020 DEBUG quirks: running focalPostInitialUpdate
2020-05-28 21:03:38,021 DEBUG running Quirks.focalPostInitialUpdate
2020-05-28 21:03:38,301 DEBUG MetaPkgs: 
2020-05-28 21:03:38,692 DEBUG no PkgRecord found for 'fonts-urw-base35', skipping 
2020-05-28 21:03:38,998 DEBUG no PkgRecord found for 'mariadb-client-10.1', skipping 
2020-05-28 21:03:38,998 DEBUG no PkgRecord found for 'mariadb-server-10.1', skipping 
2020-05-28 21:03:39,016 DEBUG no PkgRecord found for 'pgadmin4-apache2', skipping 
2020-05-28 21:03:39,016 DEBUG no PkgRecord found for 'pgdg-keyring', skipping 
2020-05-28 21:03:39,022 DEBUG no PkgRecord found for 'postgresql-12', skipping 
2020-05-28 21:03:39,102 DEBUG Foreign: 
2020-05-28 21:03:39,102 DEBUG Obsolete: apt-transport-https aptitude aptitude-common binfmt-support ca-certificates-mono certbot cli-common command-not-found-data cpp-7 cpp-8 daemon denyhosts dovecot-ldap dovecot-lmtpd dovecot-managesieved dovecot-mysql dovecot-sieve fail2ban fonts-dejavu fonts-glyphicons-halflings g++-7 galera-3 gcc-10-base gcc-7 gcc-7-base gcc-8 gcc-8-base gcc-8-multilib gir1.2-spiceclientglib-2.0 inotify-tools jenkins ldap-account-manager ldap-auth-client ldap-auth-config lib32gcc-8-dev lib32mpx2 libaopalliance-java libapache-pom-java libapache2-mod-php7.2 libapache2-mod-rpaf libapt-inst2.0 libapt-pkg5.0 libasan4 libatinject-jsr330-api-java libcdi-api-java libcilkrts5 libcommons-cli-java libcommons-io-java libcommons-lang3-java libcommons-parent-java libcrypto++-dev libcrypto++6 libcwidget3v5 libdbd-mysql-perl libdbus-glib2.0-cil libdbus-glib2.0-cil-dev libdbus2.0-cil libdbus2.0-cil-dev libdouble-conversion3 libffi7 libfstrm0 libgcc-7-dev libgcc-8-dev libgeronimo-annotation-1.3-spec-java libgeronimo-interceptor-3.0-spec-java libglib2.0-cil libglib2.0-cil-dev libglib2.0-tests libguava-java libguice-java libhawtjni-runtime-java libhiredis0.14 libicu60 libinotifytools0 libip4tc0 libip6tc0 libjansi-java libjansi-native-java libjemalloc2 libjs-bootstrap libjs-requirejs libjson-c3 libjsr305-java liblua5.1-0 liblua5.1-0-dev libluajit-5.1-2 libluajit-5.1-common libmaven-parent-java libmaven-resolver-java libmaven-shared-utils-java libmaven3-core-java libmono-btls-interface4.0-cil libmono-corlib4.5-cil libmono-i18n-west4.0-cil libmono-i18n4.0-cil libmono-posix4.0-cil libmono-security4.0-cil libmono-system-configuration4.0-cil libmono-system-core4.0-cil libmono-system-numerics4.0-cil libmono-system-security4.0-cil libmono-system-xml4.0-cil libmono-system4.0-cil libmpx2 libnode64 libnss-ldap libpam-ldap libparse-debianchangelog-perl libphodav-2.0-0 libphodav-2.0-common libplexus-cipher-java libplexus-classworlds-java libplexus-component-annotations-java libplexus-interpolation-java libplexus-sec-dispatcher-java libplexus-utils2-java libprotobuf-c1 libpython-all-dev libpython-dev libpython-stdlib libpython2-dev libpython2-stdlib libpython2.7 libpython2.7-dev libpython2.7-minimal libpython2.7-stdlib libqt5core5a libqt5glib-2.0-0 libsisu-inject-java libsisu-plexus-java libslf4j-java libspice-client-glib-2.0-8 libspice-client-glib-2.0-dev libstdc++-7-dev libubsan0 libwagon-file-java libwagon-http-shaded-java libwagon-provider-api-java libx32gcc-8-dev libxapian30 libzip5 linux-headers-5.4.0-33 linux-headers-5.4.0-33-generic linux-image-5.4.0-33-generic linux-modules-5.4.0-33-generic linux-modules-extra-5.4.0-33-generic lua-bitop lua-cjson lua5.1 luajit mariadb-client-10.3 mariadb-client-core-10.3 mariadb-common mariadb-server mariadb-server-10.3 mariadb-server-core-10.3 maven mono-4.0-gac mono-gac mono-runtime mono-runtime-common mono-runtime-sgen multiarch-support nodejs nodejs-doc nscd nslcd nslcd-utils php-fpm php-imagick php-monolog php-phpseclib php-psr-log php-zip php7.2 php7.2-cli php7.2-common php7.2-curl php7.2-fpm php7.2-gd php7.2-json php7.2-ldap php7.2-opcache php7.2-readline php7.2-xml php7.2-zip php7.3-fpm php7.3-zip php7.4 php7.4-cli php7.4-common php7.4-curl php7.4-fpm php7.4-gd php7.4-json php7.4-ldap php7.4-opcache php7.4-readline php7.4-xml php7.4-zip phpldapadmin postgresql-10 postgresql-client-10 python python-all python-all-dev python-asn1crypto python-certbot-nginx python-cffi-backend python-configparser python-crypto python-cryptography python-dbus python-dev python-entrypoints python-enum34 python-gi python-ipaddress python-keyring python-keyrings.alt python-minimal python-pip python-pip-whl python-pkg-resources python-pyicu python-secretstorage python-setuptools python-six python-wheel python-xdg python2 python2-dev python2-minimal python2.7 python2.7-dev python2.7-minimal python3-acme python3-certbot python3-certbot-nginx python3-configargparse python3-josepy python3-keyrings.alt python3-mock python3-parsedatetime python3-pip python3-requests-toolbelt python3-venv python3-virtualenv python3-wheel python3-zope.component python3-zope.event python3-zope.hookable python3.7-venv qttranslations5-l10n ragel redis-server redis-tools resolvconf rspamd spice-client-glib-usb-acl-helper ttf-dejavu-core unbound unbound-anchor virtualenv
2020-05-28 21:03:39,103 DEBUG updateSourcesList()
2020-05-28 21:03:39,123 DEBUG rewriteSourcesList() with mirror_check
2020-05-28 21:03:39,124 DEBUG ['ubuntu-minimal', 'ubuntu-standard']
2020-05-28 21:03:39,124 DEBUG Checking pkg: ubuntu-minimal
2020-05-28 21:03:39,125 DEBUG Checking pkg: ubuntu-standard
2020-05-28 21:03:39,126 DEBUG examining: 'deb http://archive.ubuntu.com/ubuntu eoan main restricted'
2020-05-28 21:03:39,126 DEBUG verifySourcesListEntry: deb http://archive.ubuntu.com/ubuntu focal main restricted
2020-05-28 21:03:39,126 DEBUG url_downloadable: http://archive.ubuntu.com/ubuntu/dists/focal/Release
2020-05-28 21:03:39,126 DEBUG s='http' n='archive.ubuntu.com' p='/ubuntu/dists/focal/Release' q='' f=''
2020-05-28 21:03:39,176 DEBUG entry 'deb http://archive.ubuntu.com/ubuntu focal main restricted' updated to new dist
2020-05-28 21:03:39,176 DEBUG examining: 'deb-src http://archive.ubuntu.com/ubuntu eoan main restricted'
2020-05-28 21:03:39,176 DEBUG entry 'deb-src http://archive.ubuntu.com/ubuntu focal main restricted' updated to new dist
2020-05-28 21:03:39,177 DEBUG examining: 'deb http://archive.ubuntu.com/ubuntu eoan-updates main restricted'
2020-05-28 21:03:39,177 DEBUG entry 'deb http://archive.ubuntu.com/ubuntu focal-updates main restricted' updated to new dist
2020-05-28 21:03:39,177 DEBUG examining: 'deb-src http://archive.ubuntu.com/ubuntu eoan-updates main restricted'
2020-05-28 21:03:39,177 DEBUG entry 'deb-src http://archive.ubuntu.com/ubuntu focal-updates main restricted' updated to new dist
2020-05-28 21:03:39,182 DEBUG running doUpdate() (showErrors=True)
2020-05-28 21:03:41,646 DEBUG openCache()
2020-05-28 21:03:42,116 DEBUG /openCache(), new cache size 8801
2020-05-28 21:03:42,117 DEBUG need_server_mode(): can not find a desktop meta package or key deps, running in server mode
2020-05-28 21:03:42,936 ERROR not handled exception:
Traceback (most recent call last):

  File "/tmp/ubuntu-release-upgrader-qzfkvt6y/DistUpgrade/DistUpgradeCache.py", line 618, in distUpgrade
    self.upgrade(True)

  File "/usr/lib/python3/dist-packages/apt/cache.py", line 388, in upgrade
    self._depcache.upgrade(dist_upgrade)

apt_pkg.Error: E:Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages.


During handling of the above exception, another exception occurred:


Traceback (most recent call last):

  File "/usr/lib/python3.7/configparser.py", line 788, in get
    value = d[option]

  File "/usr/lib/python3.7/collections/__init__.py", line 916, in __getitem__
    return self.__missing__(key)            # support subclasses that define __missing__

  File "/usr/lib/python3.7/collections/__init__.py", line 908, in __missing__
    raise KeyError(key)

KeyError: 'devrelease'


During handling of the above exception, another exception occurred:


Traceback (most recent call last):

  File "/tmp/ubuntu-release-upgrader-qzfkvt6y/focal", line 8, in <module>
    sys.exit(main())

  File "/tmp/ubuntu-release-upgrader-qzfkvt6y/DistUpgrade/DistUpgradeMain.py", line 238, in main
    if app.run():

  File "/tmp/ubuntu-release-upgrader-qzfkvt6y/DistUpgrade/DistUpgradeController.py", line 2082, in run
    return self.fullUpgrade()

  File "/tmp/ubuntu-release-upgrader-qzfkvt6y/DistUpgrade/DistUpgradeController.py", line 1991, in fullUpgrade
    if not self.askDistUpgrade():

  File "/tmp/ubuntu-release-upgrader-qzfkvt6y/DistUpgrade/DistUpgradeController.py", line 1152, in askDistUpgrade
    changes = self.calcDistUpgrade()

  File "/tmp/ubuntu-release-upgrader-qzfkvt6y/DistUpgrade/DistUpgradeController.py", line 1115, in calcDistUpgrade
    if not self.cache.distUpgrade(self._view, self.serverMode, self._partialUpgrade):

  File "/tmp/ubuntu-release-upgrader-qzfkvt6y/DistUpgrade/DistUpgradeCache.py", line 241, in wrapper
    res = f(*args, **kwargs)

  File "/tmp/ubuntu-release-upgrader-qzfkvt6y/DistUpgrade/DistUpgradeCache.py", line 668, in distUpgrade
    self.config.get("Options", "devRelease") == "True":

  File "/usr/lib/python3.7/configparser.py", line 791, in get
    raise NoOptionError(option, section)

configparser.NoOptionError: No option 'devrelease' in section: 'Options'

2020-05-28 21:03:42,936 DEBUG running apport_crash()
2020-05-28 21:03:42,936 ERROR failed to import apport python module, can't generate crash: No module named 'apport_python_hook'
2020-05-28 21:03:42,936 DEBUG can't find apport