help.nextcloud.com not accessible

When I try to access the domain I get the following message:

Safari kann die Seite „https://help.nextcloud.com“ nicht öffnen, da Safari keine Verbindung zum Server „help.nextcloud.com“ aufbauen kann.

As soon as I change the DNS, the page works without problems.

Unfortunately, as you can see in the screenshot, I can't see any blocking in the log. Where does the problem come from?