I have solved the Problem.
I have deleted the files:
/etc/rsyslog.d/incoming.conf
/etc/rsyslog.d/openmediafault-remote.conf
I have deleted all huge files under
/var/log/
With this I can re-enable rsyslog again
systemctl enable rsyslog
reboot the system
The web Interface was accessible and I could deactivate the settings under Diagnostics -> System Logs -> Settings.
Now the systems seems to be working normally.