Yes I see, the only thing I can think of is that is being set to true somewhere else? Maybe in the widget which pops up. To test this, you could put a delay before the set show mouse in your BP_Player, set it to 2 seconds, then if you open this widget, then after two seconds the mouse disapears, something else is setting it to true.
As soon as the player controller loses focus, it’s the widgets’ (if there are any) job to control cursor’s visibility. Check out this AH thread for more info and a couple of workarounds: