Hello @azizkazdal,
something seems to be broken in your local App Center cache. To fix it, you need to download the App Center data for the local cache again. This can be done with:
univention-app update
To be sure that no old cache data does interfere, you could delete the cache before with:
rm -v /var/cache/univention-appcenter/appcenter.software-univention.de/4.4/.*
I hope this helps.
Best regards,
Nico