My understanding was that in a sesquiplane layout, the single lower-spar/single attachment-point was the weak spot in both airplanes.
Oh yeah, that definitely was what the issue was and it was a sesquiplane in layout, but it was intended that the lower wing was there to support the upper wing, is all. The Nieuports are light as a feather, I guess that's what pilots liked about them, so they felt they could throw them about.