The issue is that you can't modify the position from a transform DIRECTLY. This is because the position is actually a property (not a field). Therefore, when a getter is called, it invokes a method which RETURNS a Vector3 copy which it places into the stack.

So basically what you are doing in the code above is assigning a member of the STRUCT a value that is in the stack and that is later removed.

Instead, the PROPER solution is to replace the whole property; e.g.:

using UnityEngine;
using System.Collections;
public class TEST : MonoBehaviour {
void Start () {
Vector3 newPos = NEW Vector3(10, transform.position.y, transform.position.z);
transform.position = newPos;
}
}

The issue is that you can't modify the position from a transform directly. This is because the position is actually a property (not a field). Therefore, when a getter is called, it invokes a method which returns a Vector3 copy which it places into the stack.

So basically what you are doing in the code above is assigning a member of the struct a value that is in the stack and that is later removed.

Instead, the proper solution is to replace the whole property; e.g.:

using UnityEngine;
using System.Collections;
public class TEST : MonoBehaviour {
void Start () {
Vector3 newPos = new Vector3(10, transform.position.y, transform.position.z);
transform.position = newPos;
}
}