ARFoudationで画像マーカー間にオブジェクトを載せたい。

ARFoudationを用いて、マーカー間の中心にオブジェクトを置きたいと考えています。
二つのマーカーを用意してそれぞれのマーカーの上にオブジェクトを乗せることはできました。
以下のソースコードでマーカー１と２を決めて中心点を求めオブジェクトを表示させようとしたのですが、処理が行われないという状況です。ご教示していただけると幸いです。

string name = trackedImage.referenceImage.name;
        if (name == "MARKER1")
        {
            marker1Pos = trackedImage.transform.position;
        }
 　　　　　 else if (name == "MARKER2")
        {
            marker2Pos = trackedImage.transform.position;
        }
        Vector3 center = Vector3.Lerp(marker1Pos, marker2Pos, 0.5f);
        trackedImage.transform.position = center;

C#
1using System.Collections.Generic;
2using UnityEngine;
3using UnityEngine.XR;
4using UnityEngine.XR.ARFoundation;
5
6[RequireComponent(typeof(ARTrackedImageManager))]
7public class AR : MonoBehaviour
8{
9    [SerializeField]
10    private GameObject[] placeablePrefabs;
11
12    private Dictionary<string, GameObject> spawnedPrefabs = new Dictionary<string, GameObject>();
13    private ARTrackedImageManager trackedImageManager;
14
15    Vector3 marker1Pos;
16    Vector3 marker2Pos;
17    
18
19    private void Awake()
20    {
21        trackedImageManager = FindObjectOfType<ARTrackedImageManager>();
22
23        foreach (GameObject prefab in placeablePrefabs)
24        {
25            GameObject newPrefab = Instantiate(prefab, Vector3.zero, Quaternion.identity);
26            newPrefab.name = prefab.name;
27            newPrefab.SetActive(false);
28            spawnedPrefabs.Add(prefab.name, newPrefab);
29        }
30    }
31
32    private void OnEnable()
33    {
34        trackedImageManager.trackedImagesChanged += ImageChanged;
35    }
36
37    private void OnDisable()
38    {
39        trackedImageManager.trackedImagesChanged -= ImageChanged;
40    }
41
42    private void ImageChanged(ARTrackedImagesChangedEventArgs eventArgs)
43    {
44        foreach (ARTrackedImage trackedImage in eventArgs.added)
45        {
46            UpdateImage(trackedImage);
47        }
48        foreach (ARTrackedImage trackedImage in eventArgs.updated)
49        {
50            UpdateImage(trackedImage);
51        }
52        foreach (ARTrackedImage trackedImage in eventArgs.removed)
53        {
54            spawnedPrefabs[trackedImage.name].SetActive(false);
55        }
56    }
57
58    private void UpdateImage(ARTrackedImage trackedImage)
59    {
60        string name = trackedImage.referenceImage.name;
61        
62        if (name == "MARKER1")
63        {
64            marker1Pos = trackedImage.transform.position;
65        }
66
67        else if (name == "MARKER2")
68        {
69            marker2Pos = trackedImage.transform.position;
70        }
71
72        Vector3 center = Vector3.Lerp(marker1Pos, marker2Pos, 0.5f);
73
74        trackedImage.transform.position = center;
75
76        //ここでKeyNotFoundException: The given key was not present in the dictionary.
77        //「指定されたキーが辞書に存在しませんでした」と表示される
78        GameObject prefab = spawnedPrefabs[name];
79        prefab.transform.position = center;
80        prefab.SetActive(true);
81
82        foreach (GameObject go in spawnedPrefabs.Values)
83        {
84            if (go.name != name)
85            {
86                go.SetActive(false);
87            }
88        }
89    }
90}