Thanks for the file. It helps to understand how RailClone aligns and bevels objects on a corner. basically, when Bevel Corner is enabled, the full width of the corner segment is used on the outside of a corner. This means that if the corner is a lot shorter on the X-axis than on the Y-axis, you will lose some of the geometry due to the bevel. You can see that is happening in the image below:
To counter this you should make the segments wider. If you also need to use different widths on the Internal and External corners, then I would recommend using a Conditional node with the following parameters
In that way, you can avoid the need to assign material IDs.
I hope that helps,