Hi,
I've recently encountered a similar problem, I would like to share some information.
First, if your Fiori box and S/4HANA were installed in separated systems, then you'll need a Web Dispatcher to use the Design Studio App to query CDS views.
Also, please share the console log information here (if you're using Chrome, simply press F12,) so that we can see more detailed information.
Regards,
Michael