Problem with a material on a tree mesh.

Hello guys.

I got a tree mesh + leaves from blender and importet it into unreal. When i open the mesh i got the two material slots i use to do the treestump and the leaves. The trunk is working correctly but the leaves just disapear. The material for the leaves is working correctly as i have tested it on the leav mesh seperated from the tree. what can that be? I did switched the material to two-sided already.

Thx in advance