After Upgrading to WP 4.3 the new Menu Customizer is not working.

I've updated to WordPress 4.3 and realize that when i hit the "save and publish" button in the new menu costomizer it does not save. Every other customizer feature seems to be working normally. I've tried deactivating every plugin and activating twentyfifteen and the issue is always there.

I'm attaching a couple of screenshots to show you what I mean.

It also displays an error in the console when I hit the "save and publish" button .

http://i.imgur.com/dvg66tD.gif

This is driving me nuts. I hope you can point me in the right direction.

I've also granted access to the artomultiplo.net website so you can see it by yourself.

THanks in advance

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