Make sure you have straight flight turned on in settings, no radius on the turns at the way points. The aircraft must hit the waypoint before it will take the photo. If there is a radius, even a zero distance, it may not take the photo.
Taking photos with Litchi is tuff but taking them with shingles is worse. Try a little Calamine lotion.
Seriously, I would love to know how to use Waypoints on my P4P but I haven't seen anything anywhere on my screen that said "Waypoints" so I wouldn't have any idea how to set them. The manual is a joke so any reference to instructions or videos would be greatly appreciated.