Hi Michael,
This is not an issue of the basemap but the GeoJSON shape file you are using. I suspect that you must be using the standard GeoJSON country file built into the Geo Map component and this probably does not support the state level for Germany. You will need to define your own Custom GeoJSON file that maps to the ISO codes for the state, for drilling down to lower levels. An example of how to implement this is described in the following post:
Design Studio Innovation Series - Topic 7: Geo Maps Part II - Zoom, Zoom, Zoom!
Regards,
Mustafa.