Problem solved, I will leave the solution I found for future users help:
installed a plugin “WP-Cron Control”, wich comes with a CPanel/Plesk command to trigger the Cron jobs on the server side, instead of WordPress side.
Now every scheduled post is published on time and SNAP Cron job soon follows with its own works.
Just trying to understand now why some posts don’t have all the social networks check boxes enabled… strange
Thanks
