From this incident report I come away with Yuneec admitting that the aircraft can be powered with an improperly mounted battery thereby allowing power loss at anytime during the flight. We all know this one and have the check in our preflight routine.
This also becomes the most likely cause as there were no other faults found from the telemetry or onboard flight logs by the manufacturer.
In other words someone failed to ensure the battery latch was fully engaged. Sure can make for an unexpected ground piercing touch down.
Side note: looking at telemetry from several dozen Yuneec craft (Breeze, Q500, H480, H520, and TH Plus) I have only seen three or maybe four total power loss cases that were attributable to something other than the battery not being latched. Those few were diagnosed by Yuneec as a failure in the FC (PX4) in H520 and very early TH Plus. Yuneec made full restitution in all of those cases I am aware of.