One more thing to check is if a wing is twisted up at the tip. This creates "wash-in" which makes that wing extremely prone to tip stalling.

I had that problem with my first YAI Edge 540 wing. If you had enough elevator control to land the plane, you had enough to cause a snap - and always in the same direction. Landings were really hair-raising events. I finally tracked it down to the wing twist. The replacement wing is straight and it is a completely different plane to fly. No snapping out at all with normal deflections.

Greg