Do you face the same issue when you attach your Sigma with the Canon EOS-1D X Mark II. You can easily understand the type of visual Defect that is the vignetting and some other characteristics appears when the Sigma lens adds to the lens.
Follow these tips to fix this unwanted issue.
- Navigate to red menu 1 and locate Lens abberation correction
- Turn Peripheral illum corr to OFF
However, the issue is not so major but following these tips you can get rid of the above mentioned problem and can enjoy you photography very well.