Hello ,
When you are exporting your .FBX object, what are the settings you have checked/unchecked for the geometry section?
For example, my default settings are:
The import settings you have when importing into the editor could also be what is causing your issue.
If you would like, you can share with me your .FBX file, if it is not too large, and I can test it here on my end. To do that you just need to Private Message me on the forums with the attached .fbx file in a zipped folder. If you are not comfortable with this approach, no problems, we can try to troubleshoot in other ways! 
Thank you,