Depending on software applications in Windows startup, taskbar can become a crowded place. Window hides inactive icon and only show active program application icons on the taskbar. Sometimes you are looking an application icon for quick access but it could be hidden because of its inactive status.
Unhide & view inactive taskbar icons
1. Right click on the taskbar and click properties option.
2. In Taskbar and start menu properties window, check or tick option next to hide inactive icons.
3. Click Apply and OK to see all active / inactive / hidden icons on the taskbar.