I got it working on a test site that I'm using. Didn't do anything special really, just followed the instructions.
But, interestingly enough, I just tried it on another site and there is an add-on conflicting with it. But, it was a custom one so not sure what may be causing your issues.
I'd suggest going through your add-ons and disable them one by one and then try and refresh the screen after each disable to see which one is causing you the issues.