Problem

I'm trying to display a Content List widget which gets its content from a stored search.

To do that I use the IBM Case Manager Builder. Like so(everything is in german, can't change that):

Where 709C6681-0000-CF28-A9D1-0660DB4E5E35 is the Version Series property in the Admin Console(ACCE).

Instead of displaying a list of documents, the widget remains white(shown by the red border).

What I already tried

1. Deleting the browser cache
2. Checking the log for any errors(there aren't any)
3. Checking if the search returns any documents(it does)
4. Creating a new stored search
5. Using the documentation provided by IBM Configuring the list of documents for the Content List widget and Content List widget incoming events
6. Used an event to fill the widget with content like this:

payload = {
 "StoredSearch": {
    "objectStoreName": "ObjectStoreXYZ",
    "vsId": "801B5D81-0000-C52D-9710-6141A0493829",
    "version": "released"
  }
};

return payload;

None of the things above have helped me to solve this problem.

Is there something that I fundamentally missunderstand about using this Widget?

Thanks in advance for any answers or help I may receive