Is the floor tile actually a grid that is part of the floor or is it a fill pattern that was added later? If it is annotation, it will never get hidden by a model component.
Another thing to check is how the base cabinet was made. Most of the OOTB content is fine, but if it was custom, then the family might not have solids in it, or those solids might be turned off in the detail level or view you are in. You can put a filled region into the family to "cover up" what is below it if the solid is not visible.
