4.3.1 Site Completely Broken

Hi guys.

I have just pushed an update on one of my WordPress blogs for 4.3.1 and the site is no longer functioning as it should. The posts are still there, but the admin panel is difficult to browse because everywhere there are elements colliding with each other:

View post on imgur.com

also all the widgets have disappeared:

View post on imgur.com

I have disabled all the plugins and the problem still persists, would really appreciate some help here… what a way to start the day.

Here are some of the error log messages:

2015/09/16 08:03:10 [error] 1432#0: *171 FastCGI sent in stderr: “PHP message: PHP Fatal error: Call to undefined method WP_Meta_Query::has_or_relation() in /var/www/wp-includes/user.php on line 713” while reading upstream, client: 89.240.192.240, server: site.com, request: “GET /wp-admin/plugins.php HTTP/1.1”, upstream: “fastcgi://unix:/var/run/php5-fpm.sock:”, host: “site.com”, referrer: “http://site.com/wp-admin/plugins.php?plugin_status=all&paged=1&s”

2015/09/16 08:05:26 [error] 1432#0: *348 FastCGI sent in stderr: “PHP message: PHP Fatal error: Call to undefined function wp_roles() in /var/www/wp-includes/user.php on line 1383” while reading response header from upstream, client: 89.240.192.240, server: site.com, request: “GET /wp-admin/update-core.php HTTP/1.1”, upstream: “fastcgi://unix:/var/run/php5-fpm.sock:”, host: “site.com”, referrer: “http://site.com/wp-admin/widgets.php”