Thanks for the file. It was very helpful and I've found the problem. It seems the objects disappear when the Generator's Y Offset is >= to the Padding Value. I'll pass this on to our development team. Meanwhile you can get around this by adding the desired offset to each of the Segment's Properties > Transform > Fixed > Translation > Y values (you could wire them together if you need to adjust them regularly), or by moving the Vertex to the middle of a spline as you've already discovered.
Please let me know if I can help further.