Weapon visibility bug

Hi, I’m facing a strange problem:
My game is a third person rpg, I have a mainhand socket on my character skeleton and a sword attached to this socket. Everything is ok while I try to preview the sword on the mainhand socket in the viewport, I can play animations and the mesh is here.
Now, when I play the game and equip this sword, the sword is invisible. BUT, the sword is here because when I turn the camera in every direction, sometime the sword is showing for something like one frame and disapear again. I checked the mesh normals but it’s not the problem.

The problem only happen with weapons because I made armor part with the same software/export parameters and they are visible when I equip them with the same process. Thanks

Nobody can help me?

Sorry for bumping but i still don’t know how to resolve this