Hi,
Generally, it's not commendable to use proxies inside of the RailClone object - as for example Slicing or Bending operations can't be performed correctly on those Segments.
Therefore I would highly suggest you to use meshes instead of proxies, as that'll avoid similar issues and actually there is no benefit to use them as internally all RailClone objects are converted to native V-Ray's instances.
Attaching screenshot showing this RC object using Editable Poly object "Base_Planks_00" instead of previous V-Ray Proxy "VRayProxy008 ...".
Hope that helps.
Best regards,