ReleaseAndCreateBuffer<T>

instancingShader.shader

  /// .... 

  #if SHADER_TARGET >= 45
      StructuredBuffer<float4> AgentPositionData;
  #endif
        
  VertexOut vert (appdata_full v, uint instanceID : SV_InstanceID) {

    #if SHADER_TARGET >= 45
      float4 data = AgentPositionData[instanceID];
    #else
      float4 data = 0;
    #endif
    
    // ... fill in VertexOut, etc...
  }
 
 
// ....

PseudoDemo.cs

class PseudoDemo { 
  private ComputeBuffer InstancingBuffer;
  private readonly uint[] InstancingArgs = new uint[5];
  private Material AgentMaterial;
  private ComputeBuffer agentPositionBuffer;
  private Vector4[] agentPositionData;
  private Mesh mesh;

  public PseudoDemo() { 
    mesh = MeshHelper.CreateQuadMesh(1); // creates a mesh with 1 quad
    AgentMaterial = new Material(Shader.Find(x));
    ReleaseAndCreateBuffer<Vector4>(ref agentPositionData, ref agentPositionBuffer, "AgentPositionData", 16);
    InstancingBuffer = new ComputeBuffer(1, InstancingArgs.Length * sizeof(uint), ComputeBufferType.IndirectArguments);
  }

  // Called every frame
  void Tick() { 
  
    // Update Buffers
    UpdateBuffers();

    // This ALWAYS returns true after Setup() has been called once -- even if the buffer isn't working and/or is throwing warning ("no buffer bound, stopping draw to prevent crash") on Metal, etc...
    bool isBound = AgentMaterial.HasBuffer("AgentPositionData");

    // Issue occurs even if you re-bind the buffer EVERY FRAME
    AgentMaterial.SetBuffer("AgentPositionData", agentPositionBuffer);
    
    // Render
      Graphics.DrawMeshInstancedIndirect(mesh, 0, AgentMaterial,
        new Bounds(Vector3.zero, new Vector3(float.MaxValue, float.MaxValue, float.MaxValue)),
        InstancingBuffer, 0, null,
        UnityEngine.Rendering.ShadowCastingMode.Off, false, 
        UILevelSelector.GO_LAYER_UI, null, UnityEngine.Rendering.LightProbeUsage.Off
      );
  }

  private void UpdateBuffers() {
    InstancingArgs[0] = (uint)mesh.GetIndexCount(0);
    InstancingArgs[1] = (uint)instanceCount;
    InstancingArgs[2] = (uint)mesh.GetIndexStart(0);
    InstancingArgs[3] = (uint)mesh.GetBaseVertex(0);

    InstancingBuffer.SetData(InstancingArgs);
    agentPositionBuffer.SetData(agentPositionData);
  }

  private void ReleaseAndCreateBuffer<T>(ref T[] bufferData, ref ComputeBuffer buffer, string bufferPropName, int bufferSize) {
    // Resize metadata array
    Array.Resize(ref bufferData, instanceCount);

    // Release buffers & create new one of correct size
    buffer?.Release();
    buffer = new ComputeBuffer(instanceCount, bufferSize);
    AgentMaterial.SetBuffer(bufferPropName, buffer);
  }
}