The problem looks like a bug that we had in the past. The problem is that the link is not resolved, because the target page is secured. Could you please confirm that? Please check if dynamic link is pointing to a secured page, make the page unsecure and check if the content is still rendered with the Item not found text. Please ensure that there is no caching, since you might see the cached content with the error message.
You may also try to upgrade to the latest version, which should fix the problem.
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