"Listen to this post" in beginning of post previews

To fix the issue and remove the button from excerpts and everything except for single pages or posts, edit tts-engine.php and on line 74 locate the beginning of this function:
public static function add_plugin_elements( $content ) {

Add this just beneath it:

if( !is_singular() ) { // check if single post or page. Using singular instead of single to also include pages.
return $content; // leaves the content alone and exits the loop
} else {

Remember to add an } to the end of the function to complete the if.