i receive updates and i hit install button and it starts to receive data but in the end it says error and system disconnected

[mir]

21.04 version
buntu@ubuntu-dell-latitude:~$ apt-cache policy pkgname
N: Unable to locate package pkgname
ubuntu@ubuntu-dell-latitude:~$

when i check manually for updates it give connection error while after starting the system, some upgrades are shown to be installed but when i hit the button of install starts working and in the end it gives error while i expect it to install the updates as it was doing in the previous version of the OS i.e 20.10

ProblemType: Bug
DistroRelease: Ubuntu 21.04
Package: ubuntu-release-upgrader-core 1:21.04.11
ProcVersionSignature: User Name 5.11.0-17.18-generic 5.11.12
Uname: Linux 5.11.0-17-generic x86_64
ApportVersion: 2.20.11-0ubuntu65
Architecture: amd64
CasperMD5CheckResult: unknown
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Tue May 25 19:08:31 2021
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
Symptom: dist-upgrade
UpgradeStatus: No upgrade log present (probably fresh install)