Hornet

Hello to everyone, this being my first post on this forum. I have a X-H1 with a 23mm f2 lens which sometimes on f16 when shooting sunny landscapes with blue skies I get one or two small blue circles. I don't have this problem at any other aperture. The only thing I can think of is that there is an aberration somewhere within the lens. I would be extremely grateful if anyone could give me some pointers to what the problem is. Other than that the X-H1 is brilliant. regards, Hornet