The more important plot to look at is the Flight Detail. In the Flight Detail you can see the red and black traces. This shows areas where the RC signal dropped out, likely due to obstruction or poor antenna pointing. If there is no RC signal (or it is bad) the app will not be able to trigger images as the aircraft flies through the waypoints.
To keep this from happening make sure you have a clear view of the aircraft as it flies and that your antenna are oriented properly according to your aircraft's manual.