SCNParticleSystem Crash - ios

Question

I add stock smoke SCNParticleSystem to a node in a scene in an ARSCNView. This works as expected.
I use ARSCNView.snapshot() to capture image and process before drawing in MTKView draw() method.
I then call removeAllParticleSystems() on the main thread on node with particle system and remove the node from scene with removeFromParent().
I then add other nodes to the scene and eventually, the app crashes with the error validateFunctionArguments:3469: failed assertion 'Vertex Function(uberparticle_vert): missing buffer binding at index 19 for vertexBuffer.1[0].'
TheAll Exceptions break point often stops on the ARSCNView.snapshot() call.
Why is this this crashing?
What does the error mean?
How should I be adding and removing particle systems from scenes in ARSCNView's?
UPDATE:
I hooked up the MTKView subclass I use from here to a working ARKit demo with particle system and the same Vertex Function crash occurs.
Does that mean the issue is with the passthrough vertex shader function?
Why are the particle systems treated differently?
Below are the shader functions. Thanks.
#include <metal_stdlib>
using namespace metal;
// Vertex input/output structure for passing results from vertex shader to fragment shader
struct VertexIO
{
float4 position [[position]];
float2 textureCoord [[user(texturecoord)]];
};
// Vertex shader for a textured quad
vertex VertexIO vertexPassThrough(device packed_float4 *pPosition [[ buffer(0) ]],
device packed_float2 *pTexCoords [[ buffer(1) ]],
uint vid [[ vertex_id ]])
{
VertexIO outVertex;
outVertex.position = pPosition[vid];
outVertex.textureCoord = pTexCoords[vid];
return outVertex;
}
// Fragment shader for a textured quad
fragment half4 fragmentPassThrough(VertexIO inputFragment [[ stage_in ]],
texture2d<half> inputTexture [[ texture(0) ]],
sampler samplr [[ sampler(0) ]])
{
return inputTexture.sample(samplr, inputFragment.textureCoord);
}