More and more articles about this pop up

http://www.computerbild.de/artikel/cb-News-PC-Hardware-DJI-Spark-Drohnen-Problem-18604403.html

Here from Germany

https://www.google.de/amp/s/www.theverge.com/platform/amp/2017/7/25/16025426/dji-spark-drone-customer-complaints-flight-issues

We are aware of a small number of reports involving Spark drones that have lost power mid-flight. Flight safety and product reliability are top priorities. Our engineers are toroughly reviewing each customer case and working to address this matter urgently.