do-release-upgrade crashed with AttributeError in calcDistUpgrade(): 'DistUpgradeController' object has no attribute 'tasks'

[Frits Jalvingh]

Did an install that already failed once because it was spontaneously switching to ipv6 to download, then failing all downloads.
I restored the apt sources.list from the previous version, then restarted do-release-update.

That failed with this error. After that it was a bit of work to get things alive again as apt was no longer available.

ProblemType: Crash
DistroRelease: Ubuntu 20.10
Package: ubuntu-release-upgrader-core 1:20.10.12
ProcVersionSignature: Ubuntu 5.8.0-7618.19~1599238533~20.10~d281510~dev-generic 5.8.4
Uname: Linux 5.8.0-7618-generic x86_64
ApportVersion: 2.20.11-0ubuntu49
Architecture: amd64
CasperMD5CheckResult: skip
CrashDB: ubuntu
Date: Tue Oct 6 21:31:46 2020
ExecutablePath: /usr/bin/do-release-upgrade
InstallationDate: Installed on 2020-09-04 (32 days ago)
InstallationMedia: Ubuntu 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
InterpreterPath: /usr/bin/python3.8
PackageArchitecture: all
ProcCmdline: /usr/bin/python3 /tmp/ubuntu-release-upgrader-xcftkgja/groovy --mode=server --frontend=DistUpgradeViewText --devel-release
Python3Details: /usr/bin/python3.8, Python 3.8.6, python3-minimal, 3.8.2-0ubuntu2
PythonArgs: ['/usr/bin/do-release-upgrade', '--mode=server', '--frontend=DistUpgradeViewText', '--devel-release']
PythonDetails: N/A
SourcePackage: ubuntu-release-upgrader
Title: do-release-upgrade crashed with AttributeError in calcDistUpgrade(): 'DistUpgradeController' object has no attribute 'tasks'
UpgradeStatus: Upgraded to groovy on 2020-10-06 (0 days ago)
UserGroups: N/A