Hi, Dan. I just created a simple scene using the setup you described and the shadow rendered with no problem. So, my question is whether you used a DAZ primitive plane as your ground plane, or did you import it from somewhere else? Also, if you used the DAZ plane (Create:Primitive:Plane), did you by any chance change from the default material? It is possible that the material you are using on your ground plane, whether it be DAZ or imported, does not have receive shadows turned on. The default DAZ Studio material does not have this setting, it is on by default, but if you changed the material by selecting a different shader, then shadows may have somehow been turned off.
Edit: Just a thought, is your character actually standing on a plane object, or are you simply referring to the floor grid that loads with a new scene? The floor grid is not geometry, so it will not receive a shadow. Just a thought, not trying to infer that you hadn’t considered that yourself.