Part 107 UAS pilot reported a lost link with the UAS during a flight. The pilot was unable to regain control of the UAS and a fly away occurred.

Narrative

DJI Phantom 4 Pro was being used to map an agricultural field. Pix4D Capture was being used for autonomous flight. The drone took off without incident. Drone hovered at 395 ft AGL. Then the drone began mission; the drone flew between 315 to 330 degrees (NW) in a straight line to the start position. At the time of the drone beginning mission; communication was lost with Pix4D capture app on the iPad. The app remained open and didn't shut down or close.I proceeded to provide Pause/Go Home commands on the app; but the app appeared frozen as the drone icon remained still over the map and camera live feed appeared stalled. The drone was not in the location of last connection. I proceeded to use the controller and pushed the Go Home Button. I closed and restarted Pix4D app; but the drone could not be detected by the app. I waited 30 minutes at the take off location in hopes that the drone would complete the mission and come home; which it did not come home or start the mapping portion of the mission. During the process of trying to get the drone home; I lost visual location of the drone and I am unsure where it finally landed. At this time; I am not sure what could have been done to prevent the actual fly away. The drone had been inspected and cleared for use by DJI within the past 6 months.Once the drone begins mission; I might have been able to gain control using the remote controller when it was evident that I lost connection with the iPad. However; it is unclear if I even had manual control available at the point the app lost connection to the drone telemetry.