Units under the wall units are not visible in plan view.
If the render has been set to White Fill, units under other units are not visible in plan view. The render in plan view needs to be set to Wireframe to view units placed under other units. Please follow the steps below to change the render to Wireframe.
1. Within Plan view, go to View select Wireframe render.
2. Once the render has been set to Wireframe, the units under the wall units will be visible in plan view.