package lxd 3.0.3-0ubuntu1~18.04.1 failed to install"Fupgrade: new lxd package pre-installation script subprocess returned error exxit status 1

[Maximilian Kenfenheuer]

Upgrading from 18.04 to 20.04

ProblemType: Package
DistroRelease: Ubuntu 20.04
Package: lxd 3.0.3-0ubuntu1~18.04.1
ProcVersionSignature: Ubuntu 4.15.0-132.136-generic 4.15.18
Uname: Linux 4.15.0-132-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.14
Architecture: amd64
CasperMD5CheckResult: skip
Date: Mon Jan 18 13:14:02 2021
ErrorMessage: new lxd package pre-installation script subprocess returned error exit status 1
Python3Details: /usr/bin/python3.8, Python 3.8.5, python3-minimal, 3.8.2-0ubuntu2
PythonDetails: N/A
RelatedPackageVersions:
 dpkg 1.19.7ubuntu3
 apt 2.0.2ubuntu0.2
SourcePackage: lxd
Title: package lxd 3.0.3-0ubuntu1~18.04.1 failed to install/upgrade: new lxd package pre-installation script subprocess returned error exit status 1
UpgradeStatus: Upgraded to focal on 2021-01-18 (0 days ago)

[Stéphane Graber (stgraber)]

error: unable to contact snap store

This shows the reason for the failure, it's likely the system having dropped offline at the time or some other kind of networking or firewalling issues preventing your system from reaching the package store.