Oh damn, I totally forgot about this thread. I started another on the feeling software website, and after a few days I finally solved the issue: There were vertices without any bone influences. The weird thing is that with one geometry unreal crashes in this case, but when it happens on another mesh, it just screws up the influences...

I also learned that the Unreal's early October build always crashes with the example above, but at least gives an error message

assertion failed: Wedges.Num() == WedgeInfluenceIndices.Num()

I wonder if Epic will ever officially support the Collada pipeline, since internally they are still using the crappy .PSK format (afaik).