I've been working on an animation in After Effects on my PC. I'm bout 10 seconds into the animation and now when I try to add new elements (I'm trying to have a book drop onto a desk) as soon as I animate the book to move from one position to another I get a coloured patchwork flashing up for 1 frame. I'm not sure what's causing this and how to stop it? I've tried using different illustrator files and the same happens at this particular point in the edit every time. Only once I've added keyframes.