Hi,
The solution addressed to the single.php and add update class as show below. However I could not find correct place to apply this on AppDev theme. Please check below and let me know.
Thanks.
Fix Missing required field “updated”
look for the code below on your WordPress theme’s single.php file.
Find this
<span class=”post_date”><?php the_time(‘j F,Y’); ?></span>
then add “date updated” attribute to it. Your code should look like
<span class=”post_date date updated”><?php the_time(‘j F,Y’); ?></span>
A tutorial how to apply for Twenty Eleven theme
http://www.technosultants.com/blog/warning-missing-required-field-updated-wordpress