Update UCS 5.0-2 to 5.0-3 - ERROR boot disk_space


we use the UCS Server and it runs fine with no Problems. But the last Update is “stuck” it will not work.

The Logfile says this:
**** Starting univention-updater 5.0-2 with parameter=[’/usr/share/univention-updater/univention-updater’, ‘net’, ‘–updateto’, ‘5.0-3’, ‘–ignoressh’, ‘–ignoreterm’]
Checking network repository
Update to = 5.0-3
**** Downloading scripts at Mon Apr 3 12:08:22 2023
**** Starting actual update at Mon Apr 3 12:08:23 2023

Starting /tmp/tmpxn0c9axn/https:__updates.software-univention.de_dists_ucs503_preup.sh (Mo 3. Apr 12:08:23 CEST 2023):

Please check the release notes carefully BEFORE updating to UCS 5.0-3:
English version: Release notes for the installation and update of Univention Corporate Server (UCS) 5.0-3 — UCS 5.0-3 Release Notes
German version: Release Notes für die Inbetriebnahme und Aktualisierung von Univention Corporate Server (UCS) 5.0-3 — UCS 5.0-3 Release Notes

Please also consider documents of following release updates and
3rd party components.

Do you want to continue [Y/n]?
Custom preupdate script /var/lib/local-preup.sh not found
Checking disk_space … FAIL
Checking failed_ldif … OK
Checking hold_packages … OK
Checking kernel … OK
Checking ldap_connection … OK
Checking ldap_schema … OK
Checking master_version … OK
Checking minimum_ucs_version_of_all_systems_in_domain … OK
Checking overwritten_umc_templates … OK
Checking package_status … OK
Checking required_ucsschool_version … OK
Checking role_package_removed … OK
Checking slapd_on_member … OK
Checking ssh … OK
Checking system_date_too_old … OK
Checking term … OK
Checking valid_machine_credentials … OK

The system can not be updated to UCS 5.0 due to the following reasons:

Not enough space in /boot, need at least 100 MB.
This may interrupt the update and result in an inconsistent system!

This check can be disabled by setting the UCR variable 'update50/ignore_free_space' to 'yes'.
But be aware that this is not recommended!

Error: Update aborted by pre-update script of release 5.0-3

Starting univention-upgrade. Current UCS version is 5.0-2 errata618

Checking for package updates:
Checking for app updates:
Checking for release updates: found: UCS 5.0-3
Please rerun command without --check argument to install.

The Problem is, that the boot Partition has 470 MB in Size and over 300 MB are Free. We did run the Command to Purge the old Kernels that are no longer in Use but this Error is still there.

Is this a known Bug and how do we fix it?