If you're getting an error that reads, "Image upload failed. Image failed to download. Please update this in page settings", that is because the article's featured image is missing or broken.
How to Resolve The Image Uploading Failed Error
First, access the articles Page Settings by clicking the three-dot button in the top-right corner of the editor.
Scroll down to the Featured Image option and click "remove" to clear out the broken image.
Upload the image again, or an entirely new image. Or, you can leave it blank.
Save the change, then republish the page. The error should no longer occur.