(""??? is an invalid prop. It has a different number of texture vertex indexes to polygon vertex indexes. It will not be loaded into the Octane scene."),
then the plugin has detected that the prop in question is not derived from a standard OBJ file. Whilst Poser will load these geometries as is, other apps like ZBrush, 3ds max and DazStudio will load and then correct the mesh. To correct the mesh in Poser, export and re-import the prop in Studio 3D format (and copy the materials from the old to the new prop).
I will write a script which automates this process.