Suppose we have two identical oppositely charged spheres separated by some short $ x $ distance, then if we say that superposition principle holds, then at all points in space outside the conductors, the net field is the sum of field due to each. This is simple to calculate because if we look at the spheres from a region outside boundary, they sphere set up is same as a dipole.
Now, here is the problem, what is the field inside one of the spheres? Let's take the positively charged sphere, by itself it has zero field due to being a conductor and then we add the field inside that region due to negatively charged sphere.
However, this seems wrong because the positively charged conducting sphere must always zero field inside.
Hence, my question, does superposition theorem fail for regions inside conductors?