In the JS API 4.6, when attempting to add a point to the end of a ring or path of a Polygon or Polyline, the insertPoint function seems to do nothing.
graphic.geometry.insertPoint(r,p,point);
In 4.5 this works as expected.
Looking into the source, it seems that the validation is failing when adding points to the and of the point arrays (ring/path). If I override the validation function, it can get past this, but then there are other problems with the graphic not being updated correctly.