Hi, i’m having some trouble with reflections on concave surfaces in cycles and can’t find a solution so i thought i would try my luck here.
I get banding in reflections on all glossy concave surfaces, regardless of normal directions, normal smoothing, subdivisions, node types (tried with glossy, glass and mix/add with diffuse) or types of reflections (other reflected objects, cycles sky, environment texture) and it’s driving me nuts.
The bands look something like an offset in the reflection angle that occurs with every glossy bounce, meaning that reflected objects are repeated in the reflections.
Reducing or increasing bounces in the integrator removes and adds bands one at i time, where a reduction of one bounce turns one of the bands black and so on, as would be expected if the banding itself was expected? 
I’ll try uploading a screenshot from a preview render, though the problem remains with F12 render as well.
The scene contains only two colored pillars to show the repeating reflections, cycles sky as background,
the concave objects with a glossy material and their problem-free counterparts which are the same objects scaled to -1 on the Z-axis. Rotating them or moving the camera underneath them makes the banding reappear, again regardless of normal directions.
This occurs on both GPU and CPU rendering as well, any ideas about what might me happening here?
Thanks