NullReferenceException when accessing Targets from CinemachineTargetGroup

I'm trying to adjust weights of targets like:

Code (CSharp):

1.  
2. IEnumerator AdjustWeightOnDistance () {
3.     yield return new WaitForSeconds(3f);
4.  
5.     for (int i = 1; i < targetGroup.m_Targets.Length; i++) {
6.         float distance = Vector2.Distance(player.transform.position,
7.         targetGroup.m_Targets[i].target.transform.position);
8.         // ...
9. }
10.  

There are other game objects that adds and removes targets to the same TargetGroup after a specific UnityEvent. And the above method is also invoked by the same UnityEvent. So I think that these run simultaneously.

That's why I tried adding a 'WaitForSeconds' to the above method. But still I get NullReferenceException.

Event that adds, and removes members from the TargetGroup. For some reason if I switch these two event calls, I don't get the NullReferenceException.



Once the event is being invoked, it looks like the target is not properly added or removed.

 

I think now I understand the issue little better. Say we have target1, and target2. So to add target3 and to remove target2 from group, I had to remove target2 first, only then add the target3.

Doing otherway around causes 'None (Transform)' to appear in the targets list like in the picture..