I figured it out. In case anyone else comes across this issue: I import 2 separate geometry (existing/proposed) files into the project. When I went to export, the reach selection was “defaulting” to the most recent geometry (proposed) which is why when I tried to export the existing conditions it could not reference an object because it was trying to pull from a reach that was in a different geometry file. Once again, a computer program is only as good as the person running it.