It sounds that your vehicle's velocity has reached the Linear Velocity termination condition set in the Event's Simulation Controls dialog.  By default this value is set at 2 mph, so when your vehicle's velocity reaches a value less than 2 mph, the event stops.  This may appear that the vehicle does not rebound from barrier, however a simple change to the termination conditions will allow the simulation to continue.  On the menu, select Options, Simulation Controls and then set the value for Linear Velocity to 0 mph, thereby overriding the velocity termination condition.  Reset and run the event and you will now see your vehicle fully engage the barrier and rebound as expected.