Thanks for the provided info, I checked the sample models. The rollercoaster in particular.
There should be a fix on that, you can’t call a roller coaster when it only moves in the XY plane.
If you move any of the control points of the rail-line vertically. You will notice that the IK fails. I don’t know if this is due to IK limitation, Pre-calculation limiation or wrong methodology, but in theory as I understand it IK should’ve made the calculation so that the wagons continue to follow the track upon it’s change.