Geometry goes transparent when grouped

When I group geometry, it turns transparent so that it turns the same colour/pattern as the floor material, are you able to tell me why this happens. Attached is my floorplan file - the ungrouped toilet is white, but when I made a copy of it and grouped the copy (group called Toilet 1), it turned transparent. Why is that and how can I stop that from happening?
Thanking you!
202410 V1 Bathroom cabinetry.skp (1.2 MB)

Sketchup is a 3d environment, so things on the same plane fight for graphic dominance. As you see in the gif as I orbit a bit you get flashing which is called z-fighting and is two surfaces fight to be seen.
If I lift one above the other the z-fighting stops.
GIF 18-10-2024 7-57-03 PM

Sketchup is not designed as a 2d drawing tool.

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Ah thank you, yes that makes sense (I’m a beginner!). Much appreciative for the quick response :slight_smile: