MY SU31 wing failed at the same point as yours on the trailing edge. Fortunately it did not fail completely. I suspect the wing design is the same. After removing the covering I discovered what I consider a bad design in this area. I made some changes and added carbon fiber reinforcing in the corner of the aileron in the wing. I also added carbon fiber tape to the upper and lower spar about half way out on each wing half. In addition, I glassed the center section with 8oz cloth..

IMO in an attempt to make these planes light, they have sacrificed competent design.

Just my 2
Vince