Login Loop after Update 5.2-4

Hi,
update from 5.2-3 to 5.2-4

Environment: Home-Lab with 2 server, primary and backup server

After the update, I´m not longer able to login. After submitting my credentials, the application redirects me back to the login page. If I deliberately enter an incorrect password, the correct error message appears. I tried different user, the same result.

A Nextcloud instance is installed on the primary server. I also cannot longer log in there either, neither via the “Direct Login” button nor via “SSO/SAML Login.” The same behavior as on the UCS login page.

When I log in to my backup UCS, I am taken to the dashboard (=obviously the access works). However, this does not assist me much, as I must configure everything on the primary system.

I checked ucr registry entries and on my backup ucs,
portal/auth-mode=ucs
while on my primary ucs
portal/auth-mode=saml

I changed that on my primary and restarted the service univention-portal-server.service but it doesn´t work.

Samba/AD access works, Nextcloud cccess works (over Client).

Any idea or hint what is going wrong?
Thanks in advance!

hp