This generally happens every time after you refresh the page, You can follow this documentation, https://www.wpdownloadmanager.com/doc/template-files/ As documentation, you have to copy the file in the theme directory naming a folder called download-manager, then paste it in tpls>page-templates for page template or tpls>link-templates for link template. And you have to replace the [download_link] tag with <a class="btn btn-success" href="[download_url]" target="_blank">[link_label]</a> in your page/link template. Then you can see in the refresh slug key is regenerating every time after refreshing the page.
Thanks.
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