Problems with navMeshSurface

Hi Freya, 

I have a problem using shapes. Some scenes seem to be stuck in an infinity loop as soon as i started them. 

I narrowed it down to the navMeshSurface-Component of unity. I build the navmesh through code during runtime. 
The shape "polyline" works, though. 

It would be great to have a solution for this, 

best regards,
Robert

public class navbuilder : MonoBehaviour
{
public NavMeshSurface surface;

void Start()
{
surface.BuildNavMesh();
}
}