Multisite new site creation error / issue

When I create a new site in my multisite installation, it seems something is going wrong after the site creation. I can see the new site in the multisite sites. But when I want to visit the site, I get the message that the site is not yet created? Or with the wp-admin page, I get an 404 not found error.

What is going wrong? How can I solve this?

I installed with subdomains.
I looked into the wildcard settings.