I’m using devise and I still not know when exactly stopped working the sign_out, but at some point the route
gave a routing error. For the moment, until I can really understand why is not working any more, I found some solution in a forum (lost the link, sorry :-/), where someone had posted the same problem.
So here is the solution, to overwrite the DELETE method with the GET method, so you need to add to the routes.rb file the following line:
devise_for :users do get '/users/sign_out' => 'devise/sessions#destroy' end
Now the users can log out!!!