The behavior of filled regions changes in drafting views, depending on the display setting.
By default, drafting views display in hidden line. See Hidden Line Visual Style. You can change the display to wireframe if desired. See Wireframe Visual Style.
When the drafting view is in hidden line, filled regions with fill patterns hide all elements behind them. For example, if the filled region has a diagonal crosshatch pattern, and the view is in hidden line, you cannot see an element between the openings of the pattern.
If you change the display to wireframe, elements are visible behind openings in the pattern.