I think you have to remove the old shortcode and add the new one. Here's the [new version announcement](https://steemit.com/wordpress/@wordpress-tips/update-steemit-feed-for-wordpress-v-1-1-0-new-backend-many-improvements) with detailed instructions and here's [the support forum](https://wordpress.org/support/plugin/steemit-feed) where you can troubleshoot it. Hope that helps! :)