WPF ListView no scrollbar if height set to auto
I have a hunch that your ListView is inside a panel that allows it to expand vertically without limit.
If you put a ListView inside a StackPanel, for example, the ListView's height can exceed the height of the StackPanel. The ListView has increased its height to show all its items, as far as it's concerned, thus no scrollbar.
However, if you change that StackPanel to a Grid, where controls automatically try to fit themselves inside that area, the ListView will automatically have a scrollbar when it contains more items than it can display.
This will probably be solved most simply by adjusting your layout that contains the ListView.