I realize this thread is a little old, but I've had this problem twice now on the Mk7 Golf Sportwagen I was loaned while my Mk7 GTI is in the shop. I believe this to be a software issue, seems that it loses the state when going from reverse to a forward gear somehow. I haven't quite figured out how the problem is caused, but here's the procedure I'm using to resolve it. Note that the Sportwagen I'm driving at the moment is DSG, but my GTI is 6MT and I haven't had the problem there, so YMMV:
1. Put the gearbox in reverse, confirm that the camera redeploys and the video shows up on the head unit.
2. Put the gearbox in neutral, and wait. The camera should retract along with the logo.
Everything should be working again. Still get it checked-out by the dealer, but this has worked for me both times I've had it happen in the past week I've been driving the loaner.