Hi Tobias,
We have validated the reported issue and found that the dashboard service does
not get started properly, can you restart the dashboard server in IIS as in the
below image to check whether you have resolved the issue at your end.

If still you are facing any issues from your end, please
confirm the below details to proceed further from our end.
1. Can you please let us know the Dashboard Server version which you have
installed on your machine?
2. Whether the above build is a custom build or a release
version?
3. Also share the logs
from the location(C:\Syncfusion\Dashboard
Server\DashboardServer.Web\App_Data\Logs\API).