Is the magnetic force instantaneous? And, are all field lines established simultaneously? Otherwise, for example, the field line marked 'L' will take longer time to propagate than the ones above it, so there will be a net outward flux in the time when L is out and not yet in into the surface.What happens to Gauss Law then?
Are all the field lines established simultaneously, like 'L',that stretches out so far, and the straight one? If not, then the force between the magnets must increase with time.