We just pushed a fix to the responsive engine that we consider breaking. So far, when an element was set to be hidden below a certain width and the page was set to fixed width, the element could be hidden (and the option to unhide it wasn’t shown in the editor).
The release 2 fixed this. It’s a fairly minor thing to most apps, but you should check your apps aren’t displaying a new element after you update. Note that this may affect only apps whose pages are set to fixed width.