On group wall, sometimes there some posts misses out (can not show on wall) when user click Load More button. Here is the solution :
1. Go to FTP.
2. Go to directory "wp-content/plugins/youzer/includes/public/templates/activity"
3. Open file "index.php"
4. Add this script onto line 11 (under code do_action( 'bp_before_directory_activity' ); ?>)
<script>
document.cookie = "bp-activity-oldestpage=1; expires=Thu, 18 Dec 2013 12:00:00 UTC; path=/";
</script>
5. Save file.