What’s that? A completely broken configuration. Works with my browser - but checking the domain - https://check-your-website.server-daten.de/?q=bitclusive.de
http + ipv4 have a httpt status 503, https + non-www / www and ipv4 or ipv6 have a http status 403 - Forbidden.
Redirecting a subfolder there is a wrong redirect - missing slash.
But the certificate is correct, there is no error visible.
expires in 50 days bitclusive.de, chat.bitclusive.de,
upload.bitclusive.de, www.bitclusive.de - 8 entries
No chain error, no domain name error. And no mixed content warning.
Looks like there is a system that blocks some connections. May be you have a firewall or AV-software that creates an own root certificate -> then the CA is unknown.