Hi,
in order to use curves effectively there are generally 2 things to ensure:
1. You need to manually set the spline segments to a curve and the reset to a line by right clicking on them in the viewports

2. In RailClone, you should use Default > Adaptive mode and make sure that the segments restart immediately after a vertex between a line and a curve section. You can do this by wiring a segment to the corner input and choosing an appropriate vertex type.
I hope that helps, if not, please feel free to upload a sample scene and I'll take a closer look.
All the best,
Paul