no scrolling in tab 'pages' InDesign version 18.0

I can't scroll anymore in the tab 'pages' in te latest InDesign. In 'Show pages' I tried 'vertical' , 'horizontal' as wll 'according alternative layout'. Also when I try to scroll with 'alt'. It stops at a certain pagelevel. Very irritating. Am I the only one or have I overlooked a setting? Is it a bug? Who can help me?