Linetrace Hit Out FaceIndex 0 or -1 #linetrace (UE4-21)

Using UE4.21 (no posibilty to change that)

Hello,

I tried to get a reference from an overlapping actor.
The Actor is just a bp with an static mesh.

I ve made a Tool BP with a Pickaxe Mesh.
In front of the mesh is a Spehre Collision.
The sphere generate an Overlap event. (the hit resoult of the overlap event doesnt respond anything)
The Overlap event generates a Linetrace to the Actor
and the outhit tells me the Faceindex the linetrace has hit.

This Works Fine…Sometimes

but Sometimes the Faceindex is 0 or -1

and i dont know why

EDIT: now i knwo, the index is 0 or -1 when the trace doesnt hit anything.
but there is no systhem when he hit somthing an when not

To fix it have made a loop so he trace again and again until success but its not a good pactice i think