I wouldn't call it wing droop, it's more like the wings fold inwards toward the middle creating a gap at the belly IYKWIM? It happens with only two of my nappies (different brands) and one is snap, the other aplix.

I suspect the snap one could be fixed with a second horizontal snap, does that sound right? If so, where could I get that done? Any ideas for the aplix?

I hope someone knows what I'm talking about...