We recently had this problem reported by multiple users, and the answer was difficult to find (but full credit to @fabdulazeez at the bottom of this thread: https://community.qlik.com/t5/QlikView-App-Development/Can-t-move-sheets-in-my-app/td-p/1277710)
SOLUTION: Check to see if "Touch Screen Mode" is enabled, either because the user has toggled it or (as was our case) some users have touch-screen laptops.
When touch screen mode is enabled, you must "long press" on a sheet before you try to drag it to re-order it. Short-pressing on it will not enable the "drag" function to be able to re-order.
