After creating a sub-sumary in a List View and choosing to print it above my current fields those were simply covered by the new sub-summary space. I can see the fields are still there but I have no room to enter the sub-summary category item. Is it something I'm doing wrong?
In layout mode make sure the subsummary part of the layout is large enough to fully contain the fields you wish to display; and same for any other parts for that matter. Or if you know what you want the layout to contain you could make a new layout using the layout assistant and FM will do all the appropriate sizing for you.