Adding UV Map to Model IO MDLMesh

Question

I'm trying to generate UV map for a mesh using Model/IO. The code runs on the simulator and generates a UV map for the input mesh but when I run it on a device it crashes on

mdlMesh.addUnwrappedTextureCoordinates(forAttributeNamed: MDLVertexAttributeTextureCoordinate)

with this error displayed multiple times on the console: Can't choose for edge creation.

The fatal error that terminates the app is:

libc++abi: terminating with uncaught exception of type std::out_of_range: unordered_map::at: key not found

The code:

let asset = MDLAsset()
let allocator = MTKMeshBufferAllocator(device: device)
let zoneSize = MemoryLayout<Float>.size * 3 * mesh.vertices.count + MemoryLayout<UInt32>.size * indexCount
let zone = allocator.newZone(zoneSize)

let data = Data.init(bytes: vertexBuffer.contents(), count: MemoryLayout<Float>.size * 3 * mesh.vertices.count)
let vBuffer = allocator.newBuffer(from: zone, data: data, type: .vertex)!

let indexData = Data.init(bytes: indexBuffer.contents(), count: MemoryLayout<UInt32>.size * indexCount)
let iBuffer = allocator.newBuffer(from: zone, data: indexData, type: .index)!

let submesh = MDLSubmesh(indexBuffer: iBuffer,
                            indexCount: indexCount,
                            indexType: .uint32,
                            geometryType: .triangles,
                            material: nil)

let vDescriptor = MDLVertexDescriptor()
// Vertex Positions
vDescriptor.attributes[0] = MDLVertexAttribute(name: MDLVertexAttributePosition,
                                                format: .float3,
                                                offset: 0,
                                                bufferIndex: 0)
vDescriptor.layouts[0] = MDLVertexBufferLayout(stride: MemoryLayout<Float>.size * 3)

let mdlMesh = MDLMesh(vertexBuffer: vBuffer,
                        vertexCount: mesh.vertices.count,
                        descriptor: vDescriptor,
                        submeshes: [submesh])

mdlMesh.addAttribute(withName: MDLVertexAttributeTextureCoordinate, format: .float2)
mdlMesh.addUnwrappedTextureCoordinates(forAttributeNamed: MDLVertexAttributeTextureCoordinate)

asset.add(mdlMesh)