Christoph This is what I've got from the development tools:
This is something with your host. I found the file here:
It returns blank page and
403 forbidden. The file is definitely there, but your host is denying access and trying to add some "domain parking" junk:
Just to be sure it's there, you can try to change the file name, and if the file truly does not exist, your server would return this instead:
Either your topmost website https://nachtexpeditionen.de/ contains some
.htaccess rules that is affecting these files specifically, or this is simply a flaw with your hosting. Or maybe something with permissions? (doubtful) Ask them! My point is, you know it's there, you have the web path, and it's needs to be able to load ... Files can't load it if it can't be accessed by URL for some reason.
Just shows how it's beneficial to run the CDN version in most cases 🙂