The Edit menu > Change Bar Shape to Single Bars command only applies to poly shapes and additional reinforcing shapes. It does not apply to structural and solid shapes. The command changes line pattern, rectangular pattern and circular pattern additional reinforcing shapes, and the reinforcing directly associated with poly shapes to a series of single bar reinforcing shapes.
This command does not change the reinforcing that is associated with solid or structural shapes. If you want to change the bars associated with a solid or structural shape to single bars then first change the structural or solid shape to a poly shape.