strange bug

Hi all,

I have just exerienced an annoying bug : i wanted to import a skeletal mesh whose one of the objects (let’s call it obj A) was invisible in UE4 (i don’t need to flip the normals, they point in the right direction). Then in 3ds max i deleted this object and created a new one which i skined to the same bone in order to check if the issue was the bone, i imported in UE4 and the new object appeared, so it proved that that the issue was the obj A.

The obj A is not recognized in UE4 , why ? Hopefully its shape is very simple and i can recreate it very fast but imagine if it was a far more complexe shape, it would take me 2 hours to recreate it (with retopology tool).
So my question is : How can i easily turn a dirty object from UE4 “point of vew” to a clean one in 3ds max ?