Hi Pilou, circular arc fillets do have continuity with adjacent surfaces, but it's a Tangent/G1 level of continuity. It is normal for tangent continuity to show breaks in reflections. If you want smooth reflection lines, that needs Curvature/G2 continuity and it's not possible to get that with things constructed out of circular arcs like fillets are by default. You could try the fillet option for making a G2 blend type surface for the fillets rather than the regular circular arc fillets.

- Michael