software cache does not refresh after changes in "software and updates".

1. Ubuntu 20.04
2. unknown version of package
3. After any change in "Software & Updates" cache supposed to be refreshed
4. Cache is't refreshed and error window appears

*Note:
Looks like the problem is deeper than it seems to be. "Ubuntu software" might be also affected, it does not display available, installed software, search also doesn't work.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: ubuntu-release-upgrader-core 1:20.04.18
ProcVersionSignature: Ubuntu 5.4.0-29.33-generic 5.4.30
Uname: Linux 5.4.0-29-generic x86_64
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
CasperMD5CheckResult: skip
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Sun May 17 11:37:23 2020
InstallationDate: Installed on 2020-05-06 (10 days ago)
InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
PackageArchitecture: all
ProcEnviron:
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ubuntu-release-upgrader
Symptom: release-upgrade
UpgradeStatus: No upgrade log present (probably fresh install)