Raycast Miss, How to run ComponentSystem after subscene is loaded?

Hi, I have a basic system that creates a grid of cubes, before every cube is instantiated, I would like to do a RayCast to determine the Y coordinate to place the box. But the raycast only returns a hit after a few seconds, the first time the system runs it can't find any colliders, so I'm guessing that the system is run before the subscene is created so i can't find the floor colliders.

How can I fix this?

Code (CSharp):

1. using Unity.Entities;
2. using Unity.Mathematics;
3. using Unity.Physics;
4. using Unity.Physics.Systems;
5. using Unity.Transforms;
6. using UnityEngine;
7.  
8. public struct RotateTractorInfo : IComponentData
9. {
10.     public float Speed;
11.     public Vector3 lastKnownLocation;
12.     public Vector3 teleportPoss;
13. }
14.  
15. [UpdateAfter(typeof(RequestSceneLoaded))]
16. public class RotateTractorSpawnerSystem : ComponentSystem
17. {
18.     // Start is called before the first frame update
19.     void Start()
20.     {
21.  
22.     }
23.  
24.     // Update is called once per frame
25.     void Update()
26.     {
27.  
28.     }
29.  
30.     protected override void OnUpdate()
31.     {
32.  
33.         var collisionWorld = World.GetOrCreateSystem<BuildPhysicsWorld>().PhysicsWorld.CollisionWorld;
34.  
35.         float horizone = 2.0f;
36.         float spacing  = 4.0f;
37.         Entities.ForEach((Entity entity, ref RotateTractorInitData spawnerData) =>
38.         {
39.             float spaceStepsX = 0;
40.             float spaceStepsZ = 0;
41.             for (int x = 0; x < spawnerData.NumXCubes; ++x)
42.             {
43.                 float posX = spaceStepsX - (spawnerData.NumXCubes / 2);
44.                 spaceStepsX += spacing;
45.  
46.                 spaceStepsZ = 0;
47.                 for (int z = 0; z < spawnerData.NumZCubes; ++z)
48.                 {
49.                     float posZ = spaceStepsZ - (spawnerData.NumZCubes / 2);
50.                     spaceStepsZ += spacing;
51.                     // Actually create a rotating cube entity from the prefab.
52.                     var rotatingCubeEntity = EntityManager.Instantiate(spawnerData.RotatingCubePrefabEntity);
53.  
54.                     var initPosition = new float3(posX, horizone, posZ);
55.                     var adjustedPosition = adjustForGroundLevel(collisionWorld, initPosition);
56.  
57.                     // Set the position of the rotating cube.
58.                     EntityManager.SetComponentData(rotatingCubeEntity, new Translation { Value = adjustedPosition });
59.                     EntityManager.AddComponentData(rotatingCubeEntity, new RotateTractorInfo { Speed = spawnerData.RotationSpeed, lastKnownLocation = new float3(0f, 0f, 0f) });
60.                     EntityManager.AddComponentData(rotatingCubeEntity, new Tractorbeam.Information { TractorLocation = new Vector3(posX, horizone, posZ) });
61.                 }
62.             }
63.  
64.             // We should destroy this spawner entity because if we don't, the spawner will run again on the next frame
65.             // and spawn another NumCubes rotating cubes!
66.             EntityManager.DestroyEntity(entity);
67.         });
68.     }
69.  
70.     float3 adjustForGroundLevel(CollisionWorld collisionWorld, float3 poss)
71.     {
72.         float3 aimDir = new float3(0f, -1f, 0f);
73.         float beamDistance = 100f;
74.  
75.  
76.         var staticGeomFilter = CollisionFilter.Default;
77.         staticGeomFilter.CollidesWith = 1 << 0;
78.  
79.         var closestHit = new Unity.Physics.RaycastHit();
80.         RaycastInput castInput = new RaycastInput
81.         {
82.             Start = poss,
83.             End = poss + aimDir * beamDistance,
84.             Filter = CollisionFilter.Default
85.         };
86.  
87.  
88.             if (collisionWorld.CastRay(castInput, out closestHit))
89.             {
90.             //Dose not hit here unit a few hundred loops
91.             return closestHit.Position;
92.         }
93.  
94.         return poss;
95.     }
96. }