I've seen similar lumps on shore here in the US but there was some infill of what looked like low density foam between the lattice. I think it is some sort of man made buoyancy foam with epoxy or polyester resin used to bind together a aggregate of low density foam, the low density part hydrostatically crushes when the boat sinks maybe, but that does not explain how it wound up on shore unless the resin is close to neutrally buoyant?