Thanks for bringing this to our attention. I run some tests here and it would appear that the latest versions of Datasmith are not, as you say, importing FP instances correctly. RailCLone appears to work fine.
Unfortunately, this is not a problem we can fix as support was implemented by Epic. Please feel free to report it to them, and we'll try to get in touch with their development team too.
In the meantime, you can export objects as instances by converting FP objects using Forest Tools. They will then export like any other instanced 3ds max geometry object.
Thanks again, please let me know if you have any further questions.
All the best,