Did you go to "configure pop-up" then you have a choice of "A description from one field" or "A custom attribute display" ?
I am having the opposite problem...I would like multiple features to show in the pop-up window. It was working as desired last week (ex: points at the same location would yield a pop-up with several "pages"...one for each point), but today I only get one feature to show up in the pop-up.