Incorrect generation of the navgraph, for example, nodes are generated on the ceiling.
Troubleshooting Procedure
In the View menu, check the Point cloudNormals.
Under Point Cloud appearance, select color style = normals
If you don't see multiple colors, but only gray sparse points it means that normals were not properly generated and therefore the navgraph cannot be generated.
A three-dimensional representation of an environment, made up of many points. A point is defined by x, y and z coordinates, and it may or may not contain RGB, an intensity value, and normals.
Normals are perpendicular to the tangent plane line at a particular point on the surface. They yield especially useful information about a curved surface's characteristics but conversely can tell us much about the planarity of a flat or angular surface also. Normals can tell us the rate of change of curvature when a surface has an angular departure and tell us just how perfectly flat something is.