Uncontrolled Loops Elevator failure

Not that is adds to the discussion, but by my count there have been 7 Nimbus 4D’s that have suffered spin/spiral wings break off.
The owner of a local N4D replace a metal bracket thingy in the elevator assembly on his 18 year old glider, it was the same part number for a
Dou discus and Arcus. Lots of common parts in the tail feathers of all twin place S-H gliders. Sure would be nice to know failure mode.

To add to the possibilities. In Denmark we've had a couple of cases of poor welding joints.
One Arcus had the air brake triangle coupling to the fuselage horn fail due to poor welding quality on top of the triangle being poorly designed. The pilot got in control of the plane by pulling the other brake and landed safely. After this it turned out SH didn't know whether the right triangles were installed in our Duo. They'd been mixed up between Duo's and Arcus's and apparently they're different.
Another Duo Xlt had the airbrake pushrod separate in the fuselage due to poor welding. This didn't result in an AD.
To a worrying extent the the learning feedback in European aviation is malfunctioning. The authorities are the ones supposed to address this.