I think camera location is not replicated to server, its your client thing only.
Make server side event where you feed camera location to server.
Call it from player controller (or pawn) set last tick camera location and rotation.
Then trace on server (behind authority gate).
Another culprit herer may be fact you are using references to camera, they do not transfer at all over to another client or server (because they are in different processes/pcs, so their pointers are totally different). And that reference to camera may be invalid on server. Well this again goes back to fact that camera is not replicated.
Ps.
For getting forward vector use: reference then get forward vector out of it you do not need to use rotation as middle men.