Thanks for the question,
This would appear to be related to the import settings of Megascans geometry. Depending on your most recently used FBX settings, it is possible that the geometry is not importing with the smoothing groups. You can check this by selecting the polygons in the curb object to see if they have any smoothing groups assigned.
To fix it, you can import any FBX object using the Import option in the File menu
And then ensure that Geometry > Smoothing Groups is checked. Open the file (You can delete it again afterwards, it's just to ensure Max remembers the recent import settings)
Now the next time you import an object from Megascans, the smoothing groups should also be imported and the object will appear identically in RailClone.
I hope that helps,
p.s For many Megascans assets, only one smoothing group is used. So another quick workaround if you don't want to reimport everything is just to add a Smooth modifier and set everything to use Smoothing Group 1