ImmersalのContent Placement Sampleがビルドできない

発生している問題・エラーメッセージ

Immersalが提供しているサンプルプロジェクトのうち、ContentPlacementSampleをビルドしようとすると以下の3つのエラーが発生します。エラーの解決方法についてご教授いただきたいです。
（ContentPlacementSampleについては、こちらの公式のドキュメントで解説されています。
https://immersal.gitbook.io/sdk/unity/sample-scenes/content-placement-sample ）

ArgumentNullException: Value cannot be null.
Parameter name: key
System.Collections.Generic.Dictionary`2[TKey,TValue].FindEntry (TKey key) (at <4ba27aa039714eafa1e8892e51af2932>:0)
System.Collections.Generic.Dictionary`2[TKey,TValue].ContainsKey (TKey key) (at <4ba27aa039714eafa1e8892e51af2932>:0)
Immersal.AR.ARSpace.UnregisterSpace (UnityEngine.Transform tr, System.Int32 mapId) (at Assets/ImmersalSDK/Core/Scripts/AR/ARSpace.cs:220)
Immersal.AR.ARMap.FreeMap (System.Boolean destroy) (at Assets/ImmersalSDK/Core/Scripts/AR/ARMap.cs:167)
Immersal.AR.ARMap.OnDisable () (at Assets/ImmersalSDK/Core/Scripts/AR/ARMap.cs:462)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&) (at /Users/bokken/build/output/unity/unity/Modules/IMGUI/GUIUtility.cs:189)

ArgumentNullException: Value cannot be null.
Parameter name: key
System.Collections.Generic.Dictionary`2[TKey,TValue].FindEntry (TKey key) (at <4ba27aa039714eafa1e8892e51af2932>:0)
System.Collections.Generic.Dictionary`2[TKey,TValue].ContainsKey (TKey key) (at <4ba27aa039714eafa1e8892e51af2932>:0)
Immersal.AR.ARSpace.UnregisterSpace (UnityEngine.Transform tr, System.Int32 mapId) (at Assets/ImmersalSDK/Core/Scripts/AR/ARSpace.cs:220)
Immersal.AR.ARMap.FreeMap (System.Boolean destroy) (at Assets/ImmersalSDK/Core/Scripts/AR/ARMap.cs:167)
Immersal.AR.ARMap.OnDestroy () (at Assets/ImmersalSDK/Core/Scripts/AR/ARMap.cs:467)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&) (at /Users/bokken/build/output/unity/unity/Modules/IMGUI/GUIUtility.cs:189)

MissingReferenceException: The object of type 'ARMap' has been destroyed but you are still trying to access it.
Your script should either check if it is null or you should not destroy the object.
Immersal.AR.ARMap.InitializeMesh (UnityEngine.Vector3[] pointPositions) (at Assets/ImmersalSDK/Core/Scripts/AR/ARMap.cs:265)
Immersal.AR.ARMap.LoadMap (System.Byte[] mapBytes, System.Int32 mapId) (at Assets/ImmersalSDK/Core/Scripts/AR/ARMap.cs:218)
System.Runtime.CompilerServices.AsyncMethodBuilderCore+<>c.<ThrowAsync>b__7_0 (System.Object state) (at <4ba27aa039714eafa1e8892e51af2932>:0)
UnityEngine.UnitySynchronizationContext+WorkRequest.Invoke () (at /Users/bokken/build/output/unity/unity/Runtime/Export/Scripting/UnitySynchronizationContext.cs:153)
UnityEngine.UnitySynchronizationContext.Exec () (at /Users/bokken/build/output/unity/unity/Runtime/Export/Scripting/UnitySynchronizationContext.cs:83)
UnityEngine.UnitySynchronizationContext.ExecuteTasks () (at /Users/bokken/build/output/unity/unity/Runtime/Export/Scripting/UnitySynchronizationContext.cs:107)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&) (at /Users/bokken/build/output/unity/unity/Modules/IMGUI/GUIUtility.cs:189)