ok. i did some test today morning and i guess i found a solution for now.
if i “drag and drop” into unreal folder (wherevere you choose to store your assets) and i use re-import after, it will work fine.
i already did many changes to my mesh like adding vertex, edge loops and even change UV coordinate. and the mesh still be reimported with changes as well.
i also noticed that when you use drag and drop instead of file-> import into level (that create the bug) the assets dosent create blueprint file. and fbx root file. not sure if this is where the problem are.
I tested this all morning so im not sure this work around it really resolve the issue. but for now it works for me.
i even think this is a bug between Blender and Unreal.
im using blender 2.79 and unreal 4.16.3
hope this helps someone out there.