Could you try the following:
- Install and activate Jetpack
- Go to Settings > Sharing, and add some sharing buttons
- Save your changes, and check that the buttons appear at the bottom of your posts.
- Now, install and activate the "Sharing buttons shortcode for Jetpack" plugin
- Go to Posts >All Posts, click on one of your posts, and add the following shortcode in the middle of your post content:
- Save your changes
Do you now see an extra set of sharing buttons appearing in the middle of your post content, where you've inserted the shortcode?