Most of the wordpress user uses jetpack plugin provided by WordPress.com. When they activate social share buttons on it, Jetpack uses Sharedaddy plugin as a social sharing module in wordpress.
Sometimes it conflicts with themes and plugins, and display social share buttons or icons twice below the post. check the screenshot below.
How to solve this?
It appears twice because, the social share plugin called twice in the post page. Jetpack inserts it at the bottom of the post and it is also called in single.php(post) template file.
var body = $( 'body' );
If you want to add it in your theme header file, then go to Appearance -> Editor now select header.php(Theme Header) from the right side (Templates).
Now copy the above code and paste it above the </header> tag. check the screenshot below.
That’s it, now update the file. If you are using any cache plugin, then delete all the cache and referesh the post page. Sharedaddy Social Share buttons or icons shows only once.