Thank you for your replies!

The crosshair works perfectly and it's not colliding with the player. Like I said, I narrowed it down to the c_trace. When I comment it, the movement works perfectly (the crosshair does not anymore, of course). Also if I put a wait(1); there it kind of works but with skipping frames. So it must be about timing somehow (the c_traces trace at the exact same time or something like that).

skill3 is the player's health and skill50 is the state of the gun draw animation cycle (so the dot appears when he's drawn his gun to a certain extent). I already replaced it with while(1), etc. so that's not the problem (it also works perfectly so far).