Metallic map exporting black

Hi I have two metallic maps that I want to export out of Substance Painter. 

Below are three maps the first map is the metallic map of a door and the white specs are nails. So this map is working as it should. The second map (when exported) is totally black however the screenshot below clearly shows that there are areas of metal in the map but when I export it, unlike the door that shows the metal nails the second map only exports as having no metal in the model when it does. What am I doing wrong?