Thank you, it works
I spend so many hours on this problem, and that -- was the whole thing xD

Just an other question out of curiosity (not important for my project, but something i don't understand):
Is 3dgs cheating with c_trace and getting the nearest vertex?
If I have a face and i trace it with c_trace, the hit.vertex index is always the same, even if I trace nearer on an other vertex of that face