There’s a couple ways to fix it. First head over to your Appearance > Customize page and click the Front Page Background Images tab. On this page make sure and delete the background image if you’re not using one for that section.
I noticed this doesn’t happen on the Main Demo, so I assume that maybe you attempted to upload an image sometime in the past and it didn’t show up? Sometimes if you upload an image and it doesn’t upload all the way, or if you delete the image file without removing it from the customize page it will still attempt to link to that image when the site is loaded.
Let me know if that fixes it. If it doesn’t, then I can show you how to delete a small part of the code in the output.php file. Once we do that then it will definitely remove it.
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