Compute Shader Buffer output is incomplete when Appending from another AppendStructuredBuffer

Question

I am working on a placement system where I, from specific parameters find locations in a compute shader and then append these to an AppendStructuredBuffer. This works as expected. The issues stems from using the resulting buffer in another shader, which also tries to Append to a new AppendStructuredBuffer. The output from that buffer is much less than what came in.

Eventually the result is copied to a final buffer for rendering with DrawMeshInstancedIndirect.

Here is the compute shader, it just places objects on a plane.

AppendStructuredBuffer<VegetationData> _OutVegetationData;
[numthreads(32,32,1)]
void VegetationPlacement (uint3 id : SV_DispatchThreadID)
{ 

VegetationData data;
float2 remappedVal;
Remap_float(float2(id.x, id.y), float2(0,512), float2(-256, 256), remappedVal);    
data.position = half4(float4(objPos, 0) + float4(float3(remappedVal.x, 0, remappedVal.y), 1));
data.normals = half3(0,1,0);
data.scale = 1;
_OutVegetationData.Append(data);
        
return;

And the dispatch - which is run in Update, the shader has been instanced in a start function.

void Update()
{
foreach (var vegetation in terrain.VegetationsOnTerrain)
            {
                if (vegetation.vegetationDataBuffer == null)
                {
                    vegetation.vegetationDataBuffer = new ComputeBuffer(512*512, 16 + 28, ComputeBufferType.Append);
                    vegetation.vegetationComputeShaderInstance.SetBuffer(vegetation.vegetationKernel, "_OutVegetationData", vegetation.vegetationDataBuffer);
                    vegetation.vegetationComputeShaderInstance.SetVector("objPos", terrain.transform.position);
                    vegetation.vegetationDataBuffer?.SetCounterValue(0);  
           vegetation.vegetationComputeShaderInstance.Dispatch(vegetation.vegetationKernel,
                    (int)512/32,
                    (int) 512 / 32,
                    (int) 1);
                }
            }

How it should looks

I then have another compute shader which uses that buffer as a StructuredBuffer to read from, and then fills another AppendStrucuredBuffer which will eventually have some culling happening here. This is the second compute shader:

StructuredBuffer<VegetationData> _InVerticeData;
AppendStructuredBuffer<VegetationData> _OutVegetationData;
[numthreads(32,32,1)]
void LevelOfDetail (uint3 id : SV_DispatchThreadID)
{
_OutVegetationData.Append(_InVegetationData[id.x*id.y]);
return;
}

Here is how I invoke the second computeshader. It is run just after the first shader's dispatch.

The AppendStrcturedBuffer from the first shader is set in the second compute shader as a StructuredBuffer "_InVegetationData".

foreach (var vegetation in terrain.VegetationsOnTerrain)
            {
                if (vegetation.vegetationLodDataBuffer == null)
                {
                    vegetation.lodComputeShaderInstance.SetBuffer(vegetation.vegetationLodKernel, "_InVegetationData", vegetation.vegetationDataBuffer);
                    
                    vegetation.vegetationLodDataBuffer = new ComputeBuffer(512 * 512, 16 + 28, ComputeBufferType.Append);
                    vegetation.lodComputeShaderInstance.SetBuffer(vegetation.vegetationLodKernel, "_OutVegetationData", vegetation.vegetationLodDataBuffer);
                    vegetation.materialInstance.SetBuffer("vegetationDataBuffer", vegetation.vegetationLodDataBuffer);                 
                    }   
            
                    vegetation.vegetationLodDataBuffer?.SetCounterValue(0);
                  vegetation.lodComputeShaderInstance.Dispatch(vegetation.vegetationLodKernel,
                    (int)512/32,
                    (int)512/32,
                    (int) 1 / 1);
                
                ComputeBuffer.CopyCount(vegetation.vegetationLodDataBuffer, vegetation.argsBuffer, 4);

            }

How it looks after using the second compute shader: notice the thinning.

The hope for a result, would be that the output of the first computeshader/buffer, but if I do not append them in the second compute shader, they will just not appear. I am thinking this is probably/definitely a matter of the GPU not finishing or something like that, but I am not quite sure. Any help will be much appreciated!

Thanks.