Indeed, in the Android app, the action to shoot a picture is based on a time lapse that relies on DJI firmware that transfers the orders from the app to the drone. For some reasons, which happens time to time and randomly, the images are not captured as frequently as set by our app according the computed time interval. This unfortunately results in missing pictures.
The problem is related to the time interval when it is too short. To avoid it, we would suggest to increase the altitude of the flight, reduce the overlap or reduce the flight speed. Additionally, it seems like this problem is more frequent when the SD card of the drone already contains pictures. Therefore we would recommend to clear and reformat the SD card before flying a mission with Pix4Dcapture.
Our developers are currently fixing this problem with DJI drones and new Android version will soon be released, probably beginning of January at the latest.
We apologize for the inconvenience.