As you said you “tried to create a new certificate”, did you mean for Apache or for the system? Because /etc/univention/ssl/ucs/cert.pem is Apache, while /etc/univention/ssl/ucsCA/ is for the root-CA certificate. In your screenshots I saw both.
Apache will not start if there is something broken, i.e. if the certificate is empty or invalid. You can find possible errors in the logfile /var/log/apache2/error.log
You may take a look at Renewing the complete SSL certificate chain and Renewing the SSL certificates
Maybe there is also a firewall problem, because at Port 80 a nginx is answering and Port 8888 is in “State closed”.