Unwanted line under images

Hi all,
I’m getting an unwanted border just along one side of an image. Strangely there’s no sign of it in the designer but when I go into preview there’s this thick grey line added. It only happens on some images and not on others. Any ideas why this is being added?

It happens whether I add the image as a BG to a section or to a div block. It’s only happening on full screen width images.

Screenshot 2023-08-03 at 11.43.43

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