The solution to this mystery will probably be found in your recorded flight data.
Go to DJI Flight Log Viewer | Phantom Help
Follow the instructions there to upload your flight record from your phone or tablet.
That will give you a detailed report of the flight.
Come back and post a link to the report it gives you.
Or .. just post the txt file here.
Then someone might be able to analyse it and give you an understanding of the cause of the incident.