separated the randomizer tag manager from the active scenario

com.unity.perception/Runtime/Randomization/Randomizers/Randomizer.cs

         /// <summary>
         /// Retrieves the RandomizerTagManager of the scenario containing this Randomizer
         /// </summary>
-        public RandomizerTagManager tagManager => scenario.tagManager;
+        public RandomizerTagManager tagManager => RandomizerTagManager.singleton;
 
         internal IEnumerable<Parameter> parameters
         {

com.unity.perception/Runtime/Randomization/Randomizers/RandomizerTag.cs

 using System;
-using UnityEngine.Experimental.Perception.Randomization.Scenarios;
 
 namespace UnityEngine.Experimental.Perception.Randomization.Randomizers
 {
     [Serializable]
     public abstract class RandomizerTag : MonoBehaviour
     {
-        ScenarioBase scenario => ScenarioBase.activeScenario;
+        RandomizerTagManager tagManager => RandomizerTagManager.singleton;
-            if (scenario)
-                scenario.tagManager.AddTag(GetType(), gameObject);
+            tagManager.AddTag(GetType(), gameObject);
-            if (scenario)
-                scenario.tagManager.RemoveTag(GetType(), gameObject);
+            tagManager.RemoveTag(GetType(), gameObject);
         }
     }
 }

com.unity.perception/Runtime/Randomization/Randomizers/RandomizerTagManager.cs

     /// </summary>
     public class RandomizerTagManager
     {
+        public static RandomizerTagManager singleton { get; } = new RandomizerTagManager();
+
         Dictionary<Type, HashSet<Type>> m_TypeTree = new Dictionary<Type, HashSet<Type>>();
         Dictionary<Type, HashSet<GameObject>> m_TagMap = new Dictionary<Type, HashSet<GameObject>>();
 

com.unity.perception/Runtime/Randomization/Scenarios/ScenarioBase.cs

 using UnityEngine.Experimental.Perception.Randomization.Randomizers;
 using UnityEngine.Experimental.Perception.Randomization.Samplers;
 using UnityEngine.Perception.GroundTruth;
-using UnityEngine.Rendering;
 
 namespace UnityEngine.Experimental.Perception.Randomization.Scenarios
 {
         bool m_SkipFrame = true;
         bool m_FirstScenarioFrame = true;
         bool m_WaitingForFinalUploads;
-        RandomizerTagManager m_TagManager = new RandomizerTagManager();
 
         IEnumerable<Randomizer> activeRandomizers
         {
 
         // ReSharper disable once InconsistentNaming
         [SerializeReference] internal List<Randomizer> m_Randomizers = new List<Randomizer>();
-
-        /// <summary>
-        /// The RandomizerTagManager attached to this scenario
-        /// </summary>
-        public RandomizerTagManager tagManager => m_TagManager;
 
         /// <summary>
         /// Return the list of randomizers attached to this scenario

com.unity.perception/Tests/Runtime/Randomization/RandomizerTests/RandomizerTagTests.cs

 using System.Linq;
 using NUnit.Framework;
 using UnityEngine;
+using UnityEngine.Experimental.Perception.Randomization.Randomizers;
 using UnityEngine.Experimental.Perception.Randomization.Scenarios;
 using Assert = Unity.Assertions.Assert;
 
             for (var i = 0; i < copyCount - 1; i++)
                 Object.Instantiate(gameObject2);
 
-            var queriedObjects = m_Scenario.tagManager.Query<ExampleTag>().ToArray();
+            var tagManager = RandomizerTagManager.singleton;
+            var queriedObjects = tagManager.Query<ExampleTag>().ToArray();
-            queriedObjects = m_Scenario.tagManager.Query<ExampleTag2>().ToArray();
+            queriedObjects = tagManager.Query<ExampleTag2>().ToArray();
-            queriedObjects = m_Scenario.tagManager.Query<ExampleTag>(true).ToArray();
+            queriedObjects = tagManager.Query<ExampleTag>(true).ToArray();
             Assert.AreEqual(queriedObjects.Length, copyCount * 2);
         }
     }