We recently tried to submit a plugin to the WordPress directory and were rejected because our plugin included mb-custom-post-type, and mb-custom-post-type includes its own copy of clipboard.min.js which is already included in WP core.
We were able to remove the mb-custom-post-type extension from our plugin and thus workaround the issue. However, you will probably want to fix this anyway so that plugins built with this extension will be allowed into the WP.org directory.
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