I've never been able to get auto updates for plugins working quite right so decided to take a look what it's doing and couldn't for the life of me see why Oxwall is even using FTP.  

So I decided to edit the plugins controller not to use FTP. 
Attached is a diff that shows what changes to make to the file /ow_system_plugins/admin/controllers/plugins.php
Good luck.
Disclaimer: use at your own risk!