In CED written in terms of field strengths there is no a notion of gauge invariance. The charge value is a constant in time parameter by definition. There is also a continuity equation that governs charge flows. So it is a sequence of definitions and physical equations. Charge of a system is not a dynamical variable, nor a function of dynamical variables. The Noether theorem has nothing to do with its conservation.
The masses, despite being constant, do not have a continuity equation in CED so they are not obliged to conserve ;-).
Edit 1: I see this question is not so easy for many. OK, the charge value of one particle is constant by definition (like mass) so its conservation is a sequence of definition. Another matter - whether the system charge is additive in particles? Does it evolve with time? Does it depend on interactions? To answer these questions, we have to employ the equations of motion. The charge continuity equation $\partial \rho /\partial t = div(\rho v)$ is valid for any v, so the additivity is an exact sequence of this equation: $\rho$ is additive in particles and a single charge is constant.
For the masses we can write such a continuity equations too but the system mass is generally not a sum of particle masses. The system mass is defined differently as it depends also on interactions.
Edit 2: The number of particles, charged or not, is also conserved in many theories. Do you really think it is a consequence of ambiguity in the potential definition?