A few people have reported this problem, at least in a couple cases due to the Windows 10 fall creators update.
Can you right click on the Task Bar icon and select Maximize or Restore?
Try starting the Task Manager (Ctrl-Shift-Esc or right click an open area of the Task Bar), switch to the Applications tab, then try right clicking the game and select the Switch To / Bring To Front / Minimize / Maximize options.