It's only usual if someone has set the default Failsafe Action to hover instead of the default settting of RTH.
If you post the recorded flight data, I can check to see what the failsafe action was set to or if something else might have been the issue.
There are a couple of options ...
1. 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 on the flight data.
Come back and post a link to the report it provides and someone might be able to analyse it and give you an understanding of the cause of the incident.
or
2. Just post the .txt file here
or
3. If you use Airdata, you can view the flight data on Airdata and post a link for the Airdata report