Blue lines to the left of image on Kindle

I searched but can’t find a reference to this, and I’m not sure if it’s a bug or something to do with formatting/compile.

I’ve inserted an image in my document using <$img:MyImageName> and when I compile for Kindle, blue lines are appearing to the left of the image:

I’ve verified the image file doesn’t have any artefacts (the transparent portion isn’t part of the image):

I’ve included other images in my MS using the $img tag and none of them have the blue lines.

Things I’ve tried:
Various file types (png, jpg, tif)
Recreating the image from scratch
Multiple insertion methods ($img tag, Insert > Image from File, Insert > Image Linked to Document, simply copying/pasting the image inline, and dragging into the text editor from Finder)
Turning on/off Preserve Formatting

I’m at a loss as to how to fix this, so any advice is greatly appreciated!