I looked all over the place for him and could hear him occasionally. Turns out he was under the map, he would shoot at me occasionally but I could not shoot him in any way. He was somewhere behind the red spawn doors.
I read that you can use eridian guns or Transfusion grenades through the red doors to kill them if you get that glitch, but it didn't work for me. Anyone else have this happen? I haven't tried it again since because it was so frustrating at the time since it had taken me a while to get through the whole round solo.