I'm assuming you will say "yes" but are you using Internet Explorer?  I know that every so often Chrome or FF will pop open and without thinking much about it a form can be opened by accident.

Maybe inspecting the seemingly empty actions panel in the browser's DOM explorer would hint at something wrong with CSS or JS? Anything wrong on the Network tab of F12 Developer Tools when you capture the traffic?

Yes, I'm using IE

You are right. Someone added a class hiding it.

Hi, I had the same problem and after saving and reopenning the workflow it worked well. Anyway, I still have a problem, configuring an action like for example "Request Approval", when I try to add a user using the catalog "Select People and Groups", the user is not added. Any ideas? thanks