Multiple calls to Graphics.DrawMeshInstancedIndirect - only draws last call

I'm trying to render large chunks of tiles using Graphics.DrawMeshInstancedIndirect. When I call it multiple times in the same frame it only seems to register the last call, like so:

Link to gif it it's broken here

Relevant code is below:

 public class DoDraw : MonoBehaviour 
 {
     BufferData[] data_ = new BufferData[2];
 
     [SerializeField]
     bool[] toDraw_ = new bool[2];
 
     [SerializeField]
     Material mat_;
 
     [SerializeField]
     int numToDraw_ = 2;
     
     private void Start()
     {
         data_[0] = new BufferData(Vector3.zero, Color.white, 10);
         data_[1] = new BufferData(Vector3.right * 11, Color.blue, 10);
     }
 
     private void Update()
     {
         for( int i = 0; i < 2; ++i )
         {
             if (toDraw_[i])
                 data_[i].Draw(mat_);
         }
     }
 }
 
 class BufferData
 {
     ComputeBuffer argsBuffer_;
 
     ComputeBuffer posBuffer_;
     ComputeBuffer colorsBuffer_;
 
     Bounds bounds_;
 
     public BufferData(Vector3 pos, Color color, int size )
     {
         bounds_ = new Bounds(pos, pos + Vector3.one * size);
 
         int count = size * size;
 
         argsBuffer_ = new ComputeBuffer(1, sizeof(int) * 5, ComputeBufferType.IndirectArguments);
         argsBuffer_.SetData(new int[] { 6, count, 0, 0, 0 });
         
         Vector3[] posData = new Vector3[count];
 
         for (int x = 0; x < size; ++x)
         {
             for (int y = 0; y < size; ++y)
             {
                 int i = y * size + x;
                 posData[i] = pos + new Vector3(x, y, 0);
             }
         }
 
         posBuffer_ = new ComputeBuffer(count, sizeof(float) * 3);
         posBuffer_.SetData(posData);
 
         Color[] colorData = new Color[count];
         for (int i = 0; i < count; ++i)
             colorData[i] = color;
 
         colorsBuffer_ = new ComputeBuffer(count, sizeof(float) * 4);
         colorsBuffer_.SetData(colorData);
     }
 
     public void Draw(Material mat)
     {
         mat.SetBuffer("posBuffer_", posBuffer_);
         mat.SetBuffer("colorBuffer_", colorsBuffer_);
 
         Graphics.DrawMeshInstancedIndirect(StaticQuadMesh.GetMesh(), 0, mat, bounds_, argsBuffer_);
     }
 }
 

This example is small and pointless, but it gives a good idea of what I want to do with much larger chunks of tiles. Am I misunderstanding something about how this works?