Hi Dominik,
It appears to me on our end that you might have recently moved your content from fotodesign.dominik-moser.de to dominik-moser.de, correct? Did you copy your database when you did that? If so, that was the source of the issue, because Jetpack needs to assign a unique ID to each URL. I do see that you disconnected and reconnected Jetpack, however, which appears to have fixed the issue. Is everything ok for you, then? Or do you need further help?