I did not understand following solution please send screenshot for unit prefab and unit script
Hi there, sorry you are having trouble. Since the course was launched, Mirror changed the way renderers are handled and enables them all on start. Please change it so the OnSelect and OnDeselect activate and deactivate the gameObject holding the selection sprite instead of the selection sprite renderer. Then enable the sprite renderer and deactivate the gameObject in the prefab.
You also need to enable the sprite in the prefab and then deactivate the game object. So when it first is instantiated it is inactive. Your work around in the code there works too.