This is known from the complaints of drone users published on the DJI support forum. As quoted from Quartz, there are at least 14 complaints related to it.
Users reported, while on the air, his DJI Spark suddenly lost power and crashed to the ground.
In some cases, the drone is nearing the ground and can be captured by the user. But some of the drones fell on the ground, wood, or even in the lake. This issue has also been reported to the DJI.
So far, it is not known what caused the collapse of drones made by this Chinese company. Some posters in the forum indicate the drone falls due to a user error.
Some other users actually shared their log drone flights and did not find anything strange before his drones fell.