Incorrect Amount Displayed

Hi, when i set the amount 20 in my example below, randomly some page only show 19.

[authors_list style=”1″ columns=”2″ amount=”20″ show_count=”no” show_title=”yes” show_bio=”yes” avatar_size=”250″ roles=”author” pagination=”yes” bio_word_trim=”50″ orderby=”last_name” order=”ASC”]

Thank you