Since 2016-02-17 our website is not available via IPv6 anymore.
Some Browsers and clients don't have a fallback to IPv4 and might not connect to our homepage.
Additionally we still use the old, self-signed certificate for our website.
If you managed to remove our (old) root certificate from your system and your browsers, you'll get a alert complaining about this cert.
We work on exchanging the certificate of our website by a public trusted Let's Encrypt certificate.