I have had two incidents where the Neo became uncontrollable.
In the first case I was flying over a pond in an area where GPS signal is spotty even with my larger drones. I was well over 10m above the water so being low to the water and confusing VPS was not a factor. Suddenly the Neo became uncontrollable and veered toward the trees and almost crashed but I was able to regain control and land. The likely cause was a brief loss of enough GPS satellites before it regained enough to resume control. I was too high for VPS to be of assistance. I had checked the compass direction on the app before launching.
The second incident resulted in a crash. I was out on lake ice just out from the beach and using electronic hand warmers on a cold winter day. The warmers had a magnet in them that allowed them to be attached together to be used as one. In an effort to get the Neo in the air and keep my hands warm, I hand launched Neo failing to check whether the drone orientation and the orientation in the app matched. With the warmers in my nearby coat pocket, it immediately took off at high speed behind me and hit a concrete barrier - the classic sign of a compass deflection. The log verified the reason for the crash.
Chris