Does it always do it throughout that whole 4th flight or is it just in parts?
When it says 'Photo' that means that Map Pilot told the camera to take a photo during that 1/10th of second update. It appearing 4 times means it tried to trigger it 4 times in that 10th of a second. The first 3 attempts failed so the app kept trying until it said it would take a photo. The line that shows the filename is what file got created on the previous 'Photo' mark.
It is likely that the SD card is starting to get more full and is taking slightly longer to write the images to disk.