We add a short script at the end of each story that you publish. This tracks the stats of your story and enables features like the image gallery.
The script should be embedded and not visible to the reader. If that is not the case, then you may have a plugin enabled that is removing a section of the code.
We advise temporarily disabling all plugins (except ours) and try to publish again. That will more than likely resolve the issue. You can then reactivate plugins one-by-one, while publishing stories to find the culprit.
From our experience, the WP-Markdown plugin can cause this.