I have redownloaded WordPress 3.8.3 http://wordpress.org/wordpress-3.8.3.zip and uploaded, overwriting all files beside the theme and plugin folder. While it is not the best solution due to DB changes from 3.9, it works perfectly fine so far. It is worth mentioning that when putting back 3.8.3, it asked me to update the DB tables. Maybe this has also reverted the DB from 3.9 to 3.8.3. Not sure and all at your own risk.
