I just upgraded to 2.8.4 from the admin panel.
Now the widgets drag'n'drop doesn't work. The cursor changes but I can't drag anything.
Also I can't change posts/pages that was published before upgrading. After I open a post, change the content and click save, the pages reloads and nothing changes. Preview doesn't work at all.
Trying to Preview or Publish a new post nothing happens. It returns back to blank TinyMCE and nothing is saved.
Disabled all plugins and re-activated them. Didn't help. :(