If you have watermarked all of your artwork images yet a particular image does not show the watermark, the most likely cause is that the image was, at some point, marked to Exclude From Watermarking and hence is not displaying the watermark.
To resolve the issue:
It may take 20 - 60 minutes for the change to update on your website.
See this FAQ for how to change CDN number if needed to make the correction show more quickly on your live website:
How do I add watermarks to my images?
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