i was able to start the apache Service (with “sudo systemctl start apache2”).
In /etc/apache2/sites-enabled/ncp.conf I replaced this:
SSLCertificateFile /etc/letsencrypt/live/nc-hostname/fullchain.pem
SSLCertificateKeyFile /etc/letsencrypt/live/nc-hostename/privkey.pem
with that:
SSLCertificateFile /etc/ssl/certs/ssl-cert-snakeoil.pem
SSLCertificateKeyFile /etc/ssl/private/ssl-cert-snakeoil.key
Now I have access to the WebInterface again. But the initial Problem still exist. Since we have the same problem I will follow the thread of @Martin_Friebe