GameObject change Position after game started

i have problem with my gameobject, everytime after i start the game, the Object's Y axis position changes on its own , can somebody explain to me why is this happening and how to handle this ?

this is the instantiation code, here i set the Y to 1.0f

 Vector3 spawn = new Vector3(spawnPointX, 1.0f, spawnPointZ);
             if (type == 1)//minion
             {
                         newArmy = (GameObject)Instantiate (Minion, spawn, Quaternion.identity);
                         script = newArmy.GetComponent<MinionBehaviour>();
             }
 

this is the initiation code in the gameobject's monobehaviour, again, i set the Y to 1.0f too here

     public virtual void InitiateArmy(int side, float x, float z){
         
         transform.position = new Vector3(x, 1.0f, z);
         //some other lengthy initialization
     }
 

this is the prefab, again, the pre-set value for Y is 1.0f, no rigidbody no gravity

and yet, when i press play, the Y position of the object is turned to 0.583333 i don't even know where the heck that number came from

can anyone explain why this is happening ? and how to handle it ? thanks