Arrowheads in arrow images are missing

This definitely seems like a bug. As a workaround you can wrap this arrow in a larger frame.

This snippet of code will export an arrow and put an image of it right next to it. The entire arrow should show up:

(async () => {
  const node = figma.currentPage.selection[0]
  const renderBounds = node.absoluteRenderBounds

  // Export a 2x resolution PNG of the node
  const bytes = await node.exportAsync({
    format: 'PNG',
    constraint: { type: 'SCALE', value: 2 },
  })

  // Add the image onto the canvas as an image fill in a frame
  const image = figma.createImage(bytes)
  const frame = figma.createFrame()
  frame.x = renderBounds.x + renderBounds.width + 20
  frame.y = renderBounds.y
  frame.resize(renderBounds.width, renderBounds.height)
  frame.fills = [{
    imageHash: image.hash,
    scaleMode: "FILL",
    scalingFactor: 1,
    type: "IMAGE",
  }]
})()

Result: