Instantiated objects are not destroying

There is a problem. I have a Spawner that instantiate Units from prefabs as GameObjects. After spawning, all units are stored in List. After certain of time I need to destroy units (not fixed time and not time-based at all, but only at will), but the script Destroy (gameObject) not working. Here is the sample of my code:

     //Spawner code fragment
         GameObject Loco1;
                     Loco1 = Instantiate (TestLoco, transform.position, transform.rotation) as GameObject;
                     UM.Units.Add(Loco1.transform.GetComponent<BasicUnitScript>().thisUnit); //adding new unit to list in UnitManager
         
         //Unit code fragment
         void OnAwake ()
             {
                 UM = GameObject.Find ("Camera").GetComponent<UnitManager> ();
                 thisUnit.gUnit = gameObject;
                 thisUnit = UM.UnitReturn (this.gameObject);
 
 //UnitManager returns to object reference to itself in the List
         public class UnitManager : MonoBehaviour {
             public List<Unit> Units = new List<Unit> ();
         public Unit UnitReturn(GameObject gUnit) 
             {
                 for(int i = 0; Units.Count > 0; i++)
                 {
                     if(gUnit == Units[i].gUnit)
                     {
                         return Units[i];
                     }
                 }
                 return null;
             }
         }
         
         //and again Unit's code sample
             public void Sell ()
             {
                 arrowMarked = false;
                 if (isSelected)
                 {
                     UM.UnitsSelected.Remove (thisUnit);
                 }
                 UM.Units.Remove (thisUnit);
                 Destroy (gameObject);
             }

What I can't understand, is that: at the same tame another specially instantiated object (3D animated arrow pointing selected unit) is destroying normally (it destroyed when unit deselected and instantiated on new select).