After updating to Wordpress 4.8 widgets stop working, I mean the textarea inside has disappeared and I read the following error in console:

```
ReferenceError: Can't find variable: wp
Global Code — widgets.php:202

```

Looking into the file I see the line causing the issue:

```
wp.mediaWidgets.init();

```

and so on. There are other blocks related to the `wp` variable but I really cannot understand why it's happening considering that I've already tried to disable all plugins without success. Any advice?

Thanks.