Thanks for prompting me to stop and think. I just started deactivating things in the scene until it saw the deck card again. Turns out that when I dismissed the panel, I didn't put it quite as far off the screen as originally. (I was experimenting with camera field of view to make the cards as large as possible for each aspect ratio, by placing the deck further to the left on 16 x 9, and the numbers kept changing). For some reason, even though the panel wasn't visible, it was obscuring the deck, which is the furthest object to the left. All fixed now!