SEL100400GM white circle in centre of images

[nickdsliced]

Hi all, 

I am new to Sony and have the A7riii with the 100-400 GM (SEL100400GM). Today I shot sunrise from a hill onto fog below. With many of my images I can see a ghosted light image circle in the middle of the frame which is round and like the shape of the lens glass. it is barely visible with no editing (RAW), but really apparent when contrast is added. The sunlight was off behind me to one side so it is not lens flare at all. It is not vignetting, unless the vignette covers 60% of the frame and leaves a perfect circle? It is very odd and unexplained (ruins the images), I've never seen this before on any other brand lenses. Has anyone experienced this before? Or know of a solution? I was on f8. Thanks everyone.  The image I have added has the contrast CRANKED up so you can see the circle obviously. It shows in Lightroom and Capture one. 

[nickdsliced]

It might be a weird optical phenomenon called glory, where the sun reflects on clouds or fog which are lower than the viewer. I'll keep an eye out in future.