When drawing the spline with the Pencil, do not lift off the tip of the Pencil from the screen between two control points. There was a forum thread a few months ago, please check it and let us know if it is the solution:
When drawing the spline with the Pencil, do not lift off the tip of the Pencil from the screen between two control points. There was a forum thread a few months ago, please check it and let us know if it is the solution: