Why am I invisible over the start/finish line?

This feature was implemented to give spectating viewers a view of the track. You can also move around with the E key or the Left Bumper on controller as well as move to specific checkpoints with the number keys on your keyboard.

When spectating, you will not be able to move off of the platform, however you can still move around on the platform for a better view of the track. Eventually, the race will end and you will be teleported to a parking lot. Make sure to brush up on the controls while you wait.