When running demos/IROS/example4_sinusoidal_terrain, the programs outputs values and every X lines prints "'NoneType' object has no attribute 'get_position'". The issue has to do with trying to update each actor's position by accessing the inner object's method "get_position" for each registered SimulatedBody.
In simulator.Simulation.add_trimesh_floor, the floor is created as a collision Trimesh object, graphics Trimesh object and then a SimulatedBody. The latter only stores reference of the actor (graphics object) but not the geom. Also, there really is no body so it's conceptually an inappropriate class.