https://www.atsb.gov.au/publications/investigation_reports/2...
"While climbing through 8,000 ft above mean sea level, the UAV experienced a series of uncommanded turns. The UAV self-recovered from the first two uncommanded turns however, the third upset resulted in the aircraft entering an uncontrolled spiral descent. Despite attempts to return to controlled flight, the UAV sustained an in-flight break-up."
I can only imagine the control systems that go into these gliders.
Fun fact, most planes are inherently stable, just like paper planes. If there is a disturbance, they will self correct most of the time. For example, glider pilots, if they do something stupid, are instructed to just let go of the controls, and the glider recovers on its own very quickly. Few ways this can go wrong: the wings start to "flap" by vibrating to a resonant frequency, in which case they need to change something, and also spiraling down towards the earth: not because the plane would not recover eventually, but because it might experience high forces that destroy them before recovery can happen.
Few planes are inherently un-stable: meaning they cannot keep flying without constant input, only examples I know of are fly-by-wire modern fighter jets (4th generation onward) and planes with weird shapes like the B2 bomber.
I don't think there is too much control put into these gliders for second to second operations, they are probably just letting it fly forward, with the control being: point it in a very general direction and don't lose contact with it.
That is why recovery from a spiral dive is something that a glider pilot usually has to do as part of a demonstration of proficiency. I get to do one every year as part of my seasonal check flights.
These high altitude, long duration UAVs have really long wings. So the control system would have to work to overcome the tendency to overbank. At some point the tendency to overbank might overcome the authority of the controls.
And if the tail controls aren't suitably sized, then the pilots won't have enough control authority to move of of the very stable ballistic arc the plane wants to travel on.