Question WorldToScreenPoint only works after entity comes on screen

So I want to display where each enemy is on the HUD when the enemies are offscreen. This works fine if the enemy has been on camera -- but typically the enemy is killed when met, so

TLDR:
the point is to show the players where the last few enemies are:

Code (CSharp):

1.  
2. // for each mob left
3. for (int i = 0; i < finalMobs.Count-1; i++)
4. {
5.      // if they have health
6.      if(finalMobs[i].health > 0){
7.           Vector3 objectLoc = _mainCamera.WorldToScreenPoint(finalMobs[i].gameObject.transform.position);
8.           Vector2 dist = new Vector2(
9.                        Vector3.Distance(new Vector3(Screen.width / 2, 0f, 0f), new Vector3(objectLoc.x, 0f,0f)),
10.                        Vector3.Distance(new Vector3(0f, Screen.height / 2, 0f), new Vector3(0f, objectLoc.y, 0f))
11.           );
12.  
13.           if(dist.x < Screen.width / 2)
14.                enemyMarkers[i].position = new Vector3(objectLoc.x, enemyMarkers[i].position.y, enemyMarkers[i].position.z);
15.  
16.          if(dist.y < Screen.height / 2)
17.               enemyMarkers[i].position = new Vector3(enemyMarkers[i].position.x, objectLoc.y, enemyMarkers[i].position.z);
18.  
19.      enemyMarkers[i].gameObject.SetActive(true);        
20.      }
21.      else{
22.           enemyMarkers[i].gameObject.SetActive(false);
23.      }
24. }

The above code works fine if the mob spawns inside the camera's view; But if the mob spawns outside the cameras view the marker doesn't follow*

Once the mob has been on camera at least once, the marker then follows*.

*follow - (stays at the edge of the screen)
Thank you for your time.