Hey peter,
I am really sorry for the delay of this reply,
I've checked in your site, it seems like that was a small bug when you created menu for display `All author`, I have attached the fix file from my reply, can you download it and replace into JoomlaFolder\administrator\components\com_easyblog\includes\router.php , and then purge all of your Sh404sef extension SEF URL from your backend, then try again, it will work fine.