Hi Alain,
These are very rare, and they usually happen when the posts have some additional content added to them, which is then removed during the singular page view. The most likely cases are either wierd shortcodes with the image URLs as contents, or some specific content blocks, which may not be printed correctly.
I will have to take a direct look to be able to tell. Please open a support ticket with this, and I will check via code debugging what exactly is printing the URLs.
Best,
Ernest Marcinko
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