I think that the projectile spawns well, but you toke this screen some secs after the projectile spawned, so its normal that if the vehicle is moving it seems like what youre saying
Moreover, your drawed line is not very well calibrated, if you see it with detail, the location of the projectile is not much diferent than your “ideal” line, so I think that this confirm my first mentioned theory.
Just fire the projectile with the vehicle stoped, if it spawns well, move the vehicle to another location, stop it and fire another projectile, it should spawn good again