can't do-release-upgrade

[prune]

Checking package manager │·················································································································································
Reading package lists... Done │·················································································································································
Building dependency tree │·················································································································································
Reading state information... Done │·················································································································································
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Calculating the changes │·················································································································································
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Calculating the changes │·················································································································································
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Could not calculate the upgrade │·················································································································································
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An unresolvable problem occurred while calculating the upgrade.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.38
ProcVersionSignature: Ubuntu 4.15.0-118.119-generic 4.15.18
Uname: Linux 4.15.0-118-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair nvidia_modeset nvidia
ApportVersion: 2.20.9-0ubuntu7.17
Architecture: amd64
CrashDB: ubuntu
Date: Mon Oct 5 08:28:26 2020
InstallationDate: Installed on 2017-10-16 (1084 days ago)
InstallationMedia: Ubuntu 16.04.3 LTS "Xenial Xerus" - Release amd64 (20170801)
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=en_CA:en
 TERM=screen
 PATH=(custom, no user)
 LANG=en_CA.UTF-8
 SHELL=/bin/bash
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2020-10-05 (0 days ago)