I would suggest putting in some debugging code (e.g. in the “begin routine” tab of a code component on your trial routine) so you can monitor how the lengths of the lists change as the experiment proceeds (it’s best to temporarily make your experiment show in a small window rather than be full-screen, so you can see the print statement output in real time). e.g.
print(f'Faces: {len(Faces)}. Scenes: {len(Scenes)}') # etc