your points (except maybe the extra vertices thing but i don't exactly know what you mean) have nothing to do with the mesh so it's unlikely that they are involved in the crash.
i think i already have found the reason for the crashes. the mesh must not be non-manifold (see screenshot above). all meshes that crash for me had non-manifold areas in them. but i only examined 2 models so there might be additional reasons.

i will have to do a mesh cleaning pass before reducing polygons but i don't know yet when i will have the time...